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Mosquito Control 
in Panama 

The Eradication of Malaria and Yellow Fever in 
Cuba and Panama 



BY 
Joseph A. Le Prince, c.e., a.m. 

Chief Sanitary Inspector, Isthmian Canal Commission 
1904-1914 

and 

A. J. Orenstein, m.d. 

Assistant Chief Sanitary Inspector, Isthmian Canal Commission 
With an Introduction by 

L. O. Howard, ll.d. 

Entomologist and Chief, Bureau of Entomology 
United States Department of Agriculture 



With 100 Illustrations 



G. P. PUTNAM'S SONS 

NEW YORK AND LONDON 

Gbe *ffmicfterbocfter pcesa 
1916 



LA-* 



Copyright, 19 16 

BY 

JOSEPH A. Le PRINCE 




Ube Ifcnicterbocfeer Press, t*ew 19orft 

FEB 17 1916 
©0I.A418849 



INTRODUCTION 

DRESIDENT^ ROOSEVELT early appreciated 
the fact that great as were the engineering 
difficulties to be surmounted in the making of the 
Panama Canal, the difficulties of sanitation would 
be fully as great, if not greater, and, before the 
first Canal Commission was appointed, he told a 
committee of the American Medical Association, 
the American Association for the Advancement of 
Science, and the New York Academy of Medicine, 
consisting of Doctor Welch and Doctor Osier of 
Baltimore, Doctor Musser of Philadelphia, Doctor 
Bryant of New York, and the writer, that it was his 
intention to seek for the best man in the world for 
the task, to pay him whatever would be necessary, 
and to give him full power. Fortunately, the man 
needed was found in the person of Colonel (now 
General) Gorgas, fresh from his triumphant clean- 
ing up of Havana with the consequent elimination 
of yellow fever and malaria. General Gorgas took 
with him from Cuba to Panama a man who 

iii 



iv Introduction 

had been his right hand in the cleaning up of 
Havana, J. Al Le Prince, the author of this 
book. 

The writer well remembers one morning when, 
before starting for Panama, General Gorgas and 
Mr. Le Prince called on him at his office in Washing- 
ton to talk about mosquitoes, and the confidence 
which they felt of accomplishing their gigantic task 
was inspiring. He asked General Gorgas to have 
specimens of all the Panama mosquitoes sent to him 
for naming, and the General said, ' ' I will assign Mr. 
Le Prince to see that it is done." Upon which 
Mr. Le Prince remarked, "I will have to do it 
soon, Doctor, for in a year or so there will be no 
mosquitoes there ! ' ' 

The brilliant results of the work of General 
Gorgas and his assistants are now known over the 
whole civilized globe. It has been an object- 
lesson for the sanitarians of the world and has 
demonstrated the vitally important fact that it 
is possible for the white race to live healthfully in 
the tropics. 

And now, the whole world wants to know 
how they did it. Every detail becomes of the 
greatest interest, and, in consequence, what 
Mr. Le Prince has written here will be not only 
of great practical importance as a guide to 



Introduction v 

future work of the same character, especially 
in the tropics, but also of permanent historic 
value. 

L. 0. Howard. 
Bureau of Entomology, 
U. S. Department of Agriculture. 



CONTENTS 
PART I. ANTI-MALARIA CAMPAIGN 

CHAPTER PAGE 

I. — The Status of Knowledge of Anti- 
Malaria Work in 1904 and the 
Previous Campaign in Havana . 3 

II. — The Situation on the Isthmus in 1904, 

before American Occupation . 1 6 

III. — Meteorological and Topographi- 
cal Conditions. Topographical 
Changes and their Bearing on 
Isthmian Anopheles . . . 27 

IV. — The Species of Anopheles on the 

Isthmus ..... 43 

V. — Anopheles Propagation Areas . . 55 

VI. — Harboring Places and Food of 

Anopheles .... 83 

VII. — Flight and Attraction of Mosqui- 
toes ...... 94 

vii 



viii Contents 



CHAPTER PAGE 

VIII. — Attack on Propagation Areas by 

Filling 115 

IX. — Attack on Propagation Areas by *-" 
Drainage 122 

X. — Attack on Propagation Areas by 

Oiling 151 

XI. — Attack on Propagation Areas by 

Larvacides . . . .173 

XII. — Attack on Propagation Areas and 
Adult Mosquitoes by Natural 
Enemies . . . . .180 

XIII. — Attack on Propagation Areas by 

Clearing Bodies of Water . 190 

XIV. — Attack on Propagation Areas by ' — 
Removal of Jungle . . .195 



c. 



XV. — Screening and Practical Destruc- 
tion of Adult Anopheles in 
Houses ..... 198 

XVI. — The Results Accomplished by the 

Anti-Malaria Campaign . .218 



PART II. THE YELLOW FEVER CAMPAIGN 

I. — The Campaign in Havana . . .231 

II. — The Situation on the Isthmus before 

Sanitary Work was Started . 261 



Contents ix 

CHAPTER PAGE 

III. — Geography, Meteorology, etc., and 
their Bearing on the Presence 
of Aedes Calopus .... 268 

IV. — The First Sanitary Work Done in 

Panama — Its Purpose . . .271 

V. — The Anti-Yellow Fever Campaign 

and its Results .... 293 

VI. — Measures Taken to Keep the Isth- 
mus Free from Yellow Fever . 306 

VII. — The Value of Yellow Fever Eradi- 
cation in the Construction of 
the Panama Canal . . .314 

Index 325 

NOTE — The word mosquito refers to the Anopheles 
in Part L, and to Aedes calopus in Part II., unless 
otherwise stated. 



ILLUSTRATIONS 



Jungle Covering a Stream . 
Map of the Canal Zone 
Meteorological Tables i to 9 . 
Rainfall: Curves for 1909, 1912, 1913 
A Topographic Change : Near Empire 
Constantly Changing Topography: Near 

MlRAFLORES ...... 38 



PAGE 



Chart Showing Malaria Death-Rate at 

Havana, 1871 to 1914 . . . 13 "- 

Ant-Guards: Old Hospital at Ancon . . 18 */ 

A Ditch at Ancon: Weeds Retarding 

Water Flow 20^ 



22 1/ 
26 f 
28/^ 

37' 

/ 



Daily Change of Topography ... 40 

Blocked Water-Course Changed into an 

Anopheles Breeding Place . . 42 ' 

Aquatic Vegetation Sheltering Larvae . 48 ' 

Swamp near Balboa, Caused by Building of 

Dikes 52 1/ 

xi 



xii Illustrations 



PAGE 



The Rising Waters of Gatun Lake . 54 ^ 

Cattle on Low Pasture Lands : Panama . 56 «/ 

The Effect of Floods : Empire . . 58 •/ 

Alce United with Oil in Mat-like Masses : 

Empire 58^ 

Railroad Tie Left in a Tree by a Subsiding 

Flood 62 * 

Oiling of Breeding Places along a River- 
Bank 

Vegetation Protecting Mosquito Larvae . 

A Seepage Outcrop, Controlled by an Inter- 
cepting Tile Ditch: Ancon 

Vegetation Removed from the Edge of a 
Pond at Bohio ..... 

Result of Blocking the Rio Cardenas 

Propagation Area of Gatun Mosquito 
Influx where Mosquito Flight was 
Discovered 

Detail of Anopheles Breeding Ground 
where Flight Observations were Made 

Grass and Plants almost Covering the 
Water Surface and Protecting Mosquito 
Larvae ....... 

Diagrams Showing best Locations for 
Screened Doors 



64 


• 


66 


/ 


68 


/ 


70 


/ 


72 


• 


76 


/ 


78 


/ 


78 


/ 


87 


/ 



Illustrations xiii 

PAGE 

A nopheles Collected in the Ground Cracks 
under the houses 

The Relative Positions of Panama, Ancon, 
corozal, and mlraflores 

Mosquito Trap Attached to a Window 
Screen ....... 

Mosquito Trap (Seen from Inside the 
House) ....... 

Experiment Station : Corozal 

The Shore of Gatun Lake 

Map of Gatun: Showing Anopheles Propa- 
gation Area and Houses where Stained 
Specimens were Recaptured . 

Floating Islands Blown toward Gatun 
Lake .... 

Masses of Aquatic Plants and Floating 

Islands in Gatun Lake . . . . 102 V 

The Anopheles Breeding Ground near 

Gatun ....... 106^ 

A Device for Determining the Flight 

Direction of A nopheles . . . 108 ! 

Table Showing Number of Anopheles 

Caught in Houses at Gatun . . .110 

Staining A nopheles with Aniline Dye to 

Determine Length of Flight . . 112^ 



90 v^ 


y 
95 


96^ 


96^ 


98^ 


ioo^ x 


101 •* 


102 \/ 



XIV 



Illustrations 



Anopheles in a Mosquito-Bar Exposed to 
Air Currents at Night .... 

Cracks in a Hydraulic Fill 

Longitudinal Section and Cross-Section of 
an Intercepting Tile Drain . 

Detail of Outlet of a Tile Drain 

Plan and Side View of a Junction of Tile 
Lines ....... 

Concrete Lining of a Ditch of Small Cross- 
Section 

Reinforced Thin Concrete Lining of a 

Roadside Ditch, and Support of the 

Sliding Toe of a Hill with Condemned 

Cross-Ties ...... 

Plan and Cross-Section of a Key- Wall and 
Position of Weep-Holes 

Concrete Ditch Lining . 

Concrete Lined Ditch at Balboa 

Key-Walls to Prevent Water Leaving 
Lined Ditches ..... 

Branch Ditches ...... 

Junction of Concrete Ditches, Showing 
Splash-Wall ...... 

Concrete Lining for the Bottom of a Small 

UITCH ....... 



PAGE 

II4V 

120 1 

131/ 

135 , 

136 \/ 

138 y 



138 1/ 

i 39 / 

140 

140 



140 
141 



142 



142 



Illustrations xv 



PAGE 

Junction of a Branch Ditch with a Lined 

Ditch 143 ^ 

Burning Grass from the Side of a Ditch; 

Crude Oil Used as Fuel . . . 144 

Condition of the Ditch Two Months after 

Burning. ...... 146 v 

Ditch Cleared by Hand Labor, Showing 
Condition Two Months after Removing 
Grass 148 

A Gate to Impound Water for Flushing a 

Ditch: Empire ..... 150' 

Removal and Destruction of Larvae and 
Matted Alg.e in a Ditch by Flushing: 
Empire ....... 150K 

A Simple Form of Oil Drip . . . 158 ^ 

The Flat Lampwick Drip for Heavy Oils . 160 «/ 

Oil Drip Applied to a Hillside Stream . 162 

Oiling Obstructed Streams on Cut-Over 

Lands 164 1/ 

Brush in Valley of Pedro Miguel River . 164 / 

Application of Larvacide or Oil by Knap- 
sack Sprayer: Miraflores . . 166 ^ 

Spray Nozzles 167 v 

Field Supply Tank 168 ^ 

Oil-Cart for Applying Oil to Roadside 

Ditches 168/ 



XVI 



Illustrations 



Pack-Mules, for Oil Transportation in 
Jungle Trails 

The Larvacide Plant at Ancon . 

Removing Vegetation from Overgrown 
Streams ...... 

Screened Verandas : Ancon 

A Good Device to Prevent the Sagging of 
Screened Doors . 

Types of Screened Houses : Colon Hospital 
Grounds ...... 

Types of Screened Houses: Culebra 

Screened Cars in Railroad Construction 
Camps ....... 

Table of Malaria Incidence at Construc- 
tion Camps ...... 

Slapper, Chloroform Tube, Acetylene 
Lamp, and Pill-Box; Used in Catching 
Anopheles in Houses .... 

Mosquito Trap, with Details of Con- 
struction ...... 

Interior of Laborers' Barracks; where 
a nopheles were caught daily 

Chart Showing Percentage of Employees 
Sick with Malaria in the Wet Seasons 

OF 1911, 1912, AND I913 . 



PAGE 

170 

174 r 

192 - 
192 IS 



201 



l/ 



204 y/ 

206 V 

206 
209 

212 

214/ 

216 s 

221 V> 



Illustrations 



xvii 



PAGE 

Diagram Showing the Yearly Reduction 

of Malaria among Canal Employees . 226 ^ 

Chart Showing the Monthly Malaria 

Sick-Rate from 1906 to 19 14 . . . 228 \s 

Map of Havana; Showing the Yellow 

Fever District ..... 236X 

Chart Showing the Prevalence of Yellow 

Fever in Havana, Cuba .... 244 f 

Chart Showing Yellow Fever Cases on the 

Isthmus from 1881 to 1889 . . . 264 )/ 

Part of the Panama Fumigation Brigade . 284^" 

Screened Vestibule Door .... 286 S 

A Poorly Constructed Eave-Trough . . 288 V 

A Clogged Eave-Trough .... 288 

Diagram of a Firmly Supported Eave- 
Trough 289 /* 

A Firmly Supported Eave-Trough with a 
Good Slope ...... 290 

Mosquito-Proof Water Barrel . 

A Short Length of Eave-Trough Used over 
a Doorway ...... 



S 



290 S 
310^ 



PART I 

Anti-Malaria Campaign 



CHAPTER I 

THE STATUS OF KNOWLEDGE OF ANTI-MALARIA 
WORK IN I904 AND THE CAMPAIGN AT HAVANA 

r ~PHE anti-malaria work of importance accom- 
* plished previous to 1904 was that done by 
Colonel Gorgas in Cuba and Sir Ronald Ross in the 
British Colonies in the East. 

The necessity for mosquito control has been 
appreciated since it was first demonstrated that 
some mosquitoes may transmit disease. Since 
1900 great progress has been made in the study of 
the life history and habits of mosquitoes. As a 
result, we find remarkable differences in habits, 
even among species of the same genus. The 
determination of such facts is of great importance 
in the economic control or eradication of the dis- 
ease-conveying species, and also in that of other 
genera that affect personal comfort or real estate 
values. 

It is realized that conditions pertaining to 
Anopheles control on the Isthmus and the habits 

3 



4 The Control of Mosquitoes 

of the species encountered may differ from those 
which will be found elsewhere, and that methods of 
procedure for malaria control must be modified 
accordingly ; but if in a large territory like Panama, 
where conditions are most favorable for the 
multiplication of mosquitoes every day in the 
year, malaria has been controlled at a reasonable 
cost, the methods which accomplished the change 
are worth consideration. 

Health officials from foreign countries have 
visited the Isthmus to obtain practical infor- 
mation in order to apply this later in malaria and 
yellow fever eradication abroad. 

Much interest was shown by the thousands of 
Americans who visited the canal, and many of 
them asked why the same class of work could not 
be attempted in malarial districts in the United 
States, and also sought information about the 
work accomplished and methods of procedure. 

The canal will be used by the commerce of all 
nations, and the progress made in sanitation in 
Cuba and Panama will have far-reaching effects. 

The character of the work at Havana was quite 
different from that required on the Isthmus. The 
general situation resembled more closely the condi- 
tions and drainage problems occurring in the 
southern part of the United States, and subtropical 



The Campaign at Havana 5 

countries not having an excessive annual rainfall. 
This work was started in 1901 when the yellow 
fever campaign was well advanced. No anti- 
malaria work had been attempted elsewhere pre- 
vious to the Cuban anti-malaria campaign. Ross 
started his practical field work in the East at the 
same time that work was begun in Havana. There 
was no previously acquired information available 
on the subject nor any known practical methods 
that could be followed, or that could assist those in 
charge of operations. At that time, very little was 
known regarding the habits and life history of 
Anopheles. It was practically all pioneer work, 
and improvements and methods of procedure were 
devised as the work progressed. Years of subse- 
quent experience have shown that for pioneer work 
the scheme was excellent. 

A survey was first made to determine the princi- 
pal sources of Anopheles affecting Havana and its 
outlying suburbs. The most important propaga- 
tion areas received first attention. Treatment of 
pools with oil having a paraffin base was tested. 
As the wet places harboring Anopheles were widely 
scattered over a large area, a covered wagon was 
used for transporting laborers, tools, and oil to 
control as much territory as possible with the 
small force employed. The plan of oiling was 



6 The Control of Mosquitoes 

arranged so that areas were not treated at regular 
intervals, but when Anopheles and other mosquito 
larvae were present. 

The system of inspection was well carried out, 
and inspections were independently checked at 
proper intervals. The result of Anopheles eradi- 
cation by use of oil was fairly good, and better 
results were obtained than expected under the 
climatic and topographical conditions on the 
Isthmus. Very few topographical changes were 
being made in the vicinity of Havana. The class of 
labor available was very good, and fairly intelli- 
gent. The wages paid to the men in the Anoph- 
eles brigade were a little above average laborer's 
wages; this enabled the sanitary department to 
obtain the best class of labor and to retain it. The 
men used their heads as well as their hands, and 
worked with interest. The unit cost of ditching 
and of oil application was very low, and much was 
saved by the proper selection and payment of 
labor. Poor labor on anti-malaria work is most 
unsatisfactory, and no saving has ever been made 
by its employment. 

It was soon found that there were disadvantages 
in using oil, as well as much repetition of work that 
could be eliminated. As rapidly as the limited 
appropriation would allow, the pools costing most 



The Campaign at Havana 7 

to control were drained or filled in, and the area 
under control thus increased. Each place drained 
or filled became one less to inspect and treat. 

As time went on, the anti-Anopheles work 
consisted chiefly of draining and filling depressions 
in fields where water collected. The use of what is 
known as the "herring bone" system of ditching, 
the training of streams to more direct courses, and 
the reducing of the average wetted section of 
ditches, rapidly decreased the necessity for regular 
application of oil and for frequent inspection. 

The geological formation and topographical 
conditions were favorable. The watercourses and 
areas to be treated were often distant from one 
another, yet the streams were of fair grade, and 
most of the areas needing treatment were located 
so that they could be drained. In some cases the 
impervious surface clay rested upon a coral for- 
mation. The latter was of a porous nature, and 
absorbed a large quantity of water in a relatively 
short time. In some places where there were 
ponds, and surface drainage was out of the ques- 
tion, they were connected by one or more ditches, 
and led to shallow wells in the coral formation, 
where the water was absorbed. When one well 
was not sufficient, two or more were mad 2 and 
connected, to increase the absorbent surface. 



8 The Control of Mosquitoes 

It was found that the bottom of these wells became 
clogged with clay and silt, but that the sides 
supplied sufficient absorbent surface to give 
satisfactory results. Fish were used to keep some 
of the wells free from mosquito life ; in others, that 
frequently became dry, oil was used. Sometimes 
it was necessary to scrape well walls several times 
during the wet season to increase absorption. 

The limited funds available did not permit the 
permanent lining of ditches, although in many 
cases it would have been more economical than 
treating and maintaining them for an indefinite 
length of time. 

Anopheles production in wet areas caused by 
seepage occurs in Cuba, and one case near Havana 
was especially interesting. In 1900, a few houses 
were located near the top of the hill known as 
Jesus del Monte. Malaria prevailed among the 
tenants, and several deaths from pernicious malaria 
occurred there immediately before the undertaking 
of anti-malaria work. The hill appeared to be 
dry, and was well above the elevation of the sur- 
rounding ground. Many inspections were made to 
locate the source of Anopheles with negative results. 
It was supposed that they came from a distance, 
but an extended inspection of the surrounding 
country disproved this conclusion. 



The Campaign at Havana 9 

Finally, it was decided that the breeding place 
must be local, and the labor force was put in line, 
men eight feet apart so that every square yard of 
the hill would be seen, and no wet place, however 
small, could be missed. They marched along for 
some time before a piece of partially soft ground 
was found. There were no surface indications, 
such as a change in the vegetation or its color, 
to mark the outline of the wet area. A thin film of 
water was found to outcrop along a contour line, 
to run along the surface for a distance of about 
twenty feet, and then disappear into the ground. 
The mosquito larvae were very plentiful. A ditch 
was made above the seepage outcrop line, but 
failed to intercept the water. Two short and deep 
parallel intercepting ditches were made about nine 
feet apart, but failed to prevent the water coming 
up between the two ditches. It became evident 
that the local porous water-bearing strata were 
inclined and pointed upwards, and that a distant 
pressure was forcing the water uphill. Ditching 
was out of the question. At a small cost the 
ground affected by the surface flow was covered 
with gravel and cinders to a depth of about six 
inches, so that the mosquitoes could not reach the 
water which continued in its original path. 

Since that time the importance of hidden mos- 



io The Control of Mosquitoes 

quito-producing areas, and their relation to the 
malaria situation, has been fully appreciated by 
those engaged in anti-malaria work. Beginners 
usually learn facts by temporary failure. Soon 
after the completion of this work the adult Anoph- 
eles disappeared from the vicinity. No new cases 
of malaria occurred. The houses that had been 
so long vacant because of the prevalence of malaria 
were again occupied. When it became known that 
malaria no longer existed in that locality, it was 
plotted into lots, and has become one of the popu- 
lar residential sections of the town. Real estate 
values have advanced accordingly. 

On low flat lands where cattle were pastured, it 
was found difficult to prevent Anopheles propaga- 
tion in the water retained by hoof -prints. It be- 
came essential to prevent certain portions of fields 
from being used for grazing purposes during the 
wet season. 

It was also found that plants along the shore 
line, as well as aquatic plants, reduced the surface 
velocity of water in streams and rivers to such an 
extent as to afford protection and harboring 
places for mosquito larvae. The vegetation at the 
edges of ponds and streams was kept cut short. 
Aquatic vegetation was pulled up by the roots and 
removed. Small fish were very efficient larvae 



The Campaign at Havana n 

exterminators after the clearing and training of 
natural watercourses was accomplished. Condi- 
tions affecting growth of vegetation and algae were 
less favorable in Cuba, and, in consequence, fish 
are of more use there as destroyers of mosquito 
larvae than on the Isthmus. 

Beds of watercress in the Chinese truck gardens 
were a prolific source of Anopheles in Havana. 
The cress beds were made by erecting small dikes 
on flat land, and bringing water to them by ditches 
from nearby streams. When the enclosure was 
filled, the water was left standing for long periods. 
In order to control the situation, small wooden 
sliding gates were installed at each end of the 
watercress beds, which were flooded at frequent 
intervals for short periods, and the water then 
allowed to escape back to the stream. This 
scheme, when properly carried out, practically 
stopped Anopheles development. The gardeners 
who refused to adopt the new method were not 
allowed to grow watercress. The crops grown in 
this manner were as vigorous as those raised in the 
continuously flooded patches. 

Between the heavy showers that occur near 
Havana there are dry periods, accompanied by 
strong winds. When the ditches and watercourses 
are kept fairly free from vegetation, the heavy 



i2 The Control of Mosquitoes 

showers are often beneficial, as they remove any 
Anopheles larvae clinging to banks of ditches or 
cleared streams. The trade winds assist evapora- 
tion to a considerable extent, and help to dry the 
depressions in flat areas that hold water. The 
soil is of such a character that the trained streams 
and ditches can be kept to a proper section with 
less work than is necessary to attain this result 
at Panama. Washouts and caving of ditch banks 
did not happen as frequently. 

In many places apparently well fitted for the 
support of Anopheles larvae, they were absent; 
yet lived and developed when placed therein as 
an experiment. The reason why Anopheles eggs 
are not laid in certain areas apparently in every 
way similar to those in which larvae are found is 
yet unexplained. The season of Anopheles pro- 
duction in Cuba is much shorter and less continu- 
ous than on the Isthmus. It was largely due to 
these causes that oiling at irregular intervals gave 
satisfactory results. Conditions of soil, topo- 
graphy, and climate there do not favor the rapid 
and continuous production of mosquitoes as much 
as in the Canal Zone. 

The drainage connected with the Havana 
campaign was completed within a year of the time 
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| Deaths caused by Malaria in Havana 1871-1914 • 

Anti Malaria Campaign was Started in 1901 -Note the Curve from 1901 to 1914 

1871 to 1880 - 8415 deaths 

1881 to 1890 - 2050 " 

1891 to 1900 - 5C33 « 

1901 to 1910 - 444 " 
1911 to 1914 - 25 .. ( for 4 years^ 



1871 to 1914 ( 12,607 



In 44 years ) 



Chart showing malaria death-rate at Havana 1871 to 1914. 



13 



14 The Control of Mosquitoes 

since then has been mostly a question of economy. 
The sanitary department of the Republic of Cuba 
has continued the work started by Colonel Gorgas 
and deserves great praise for the excellent record 
it has maintained. 

To review the results of the Havana campaign, 
the records show : 

Population of Havana, 350,000. 

From 1890 to 1900, — 5643 deaths from malaria. 

From 1900 to 1910, — 444 deaths from malaria, 
with a largely increased population. 

It is interesting to note the rapidity with which 
malaria control was accomplished, as shown by the 
following table: 

TABLE OF DEATHS FROM MALARIA IN HAVANA, CUBA, 

1901 TO 1912 



Year 


No. of 
Deaths 


Year 


No. of 
Deaths 


Year 


No. of 
Deaths 


1901 
1902 
1903 
1904 


151 

77 
5i 
44 


1905 
1906 
1907 
1908 


32 
26 

23 

19 


1909 
1910 
1911 
1912 


6 

15 
12 

4 



Malarial fever is almost eliminated from Havana 
and its suburbs. 

The cost of maintaining this condition is very 



The Campaign at Havana 15 

low, and might be further reduced by lining the 
bottoms of the small streams and ditches with 
reinforced concrete, in order to lower the cost of 
cleaning and ditch maintenance. 



CHAPTER II 

THE SITUATION ON THE ISTHMUS IN I904, BEFORE 
AMERICAN OCCUPATION 

PRESIDENT ROOSEVELT appointed Colonel 
* W. C. Gorgas as Chief Sanitary Officer of the 
Isthmian Canal Commission, and it was under his 
leadership that the first sanitary survey was made. 
He established temporary headquarters for his first 
assistants at Ancon, where the French had terraced 
the hillsides and had established a hospital of 
about twenty wards. The situation selected by 
the French was excellent, but to-day, from our 
more advanced knowledge, we can readily under- 
stand why their sick-rate was so high, and can 
also realize that it would have been equally so 
under an American administration working with 
the limited knowledge pertaining to malaria pre- 
vious to the year 1900. 

At the time the American government assumed 
control of the Canal Zone, there was a succession 

of villages strung along the line of the canal ; most 

16 



The Isthmus in 1904 17 

of them close to the camps occupied by the laborers 
during the days of the French Canal Company. 
They were located apparently with reference to 
proximity to work and many were near a conven- 
ient source of water supply. At the time these 
camps were established, nothing was known regard- 
ing the transmission of malaria. Better locations 
were available, but they were in nearly all cases 
far distant from the canal. Some of the camps 
had been abandoned altogether and could not be 
reached without cutting pathways through the 
jungle. 

In some cases, where the rafters had decayed 
and the roofs had collapsed, trees with a diameter 
of ten inches were growing inside the buildings. 
The natural watercourses were overgrown by 
dense jungle, and nearly all of the villages were 
practically in the jungle itself. The French 
engineers had, for drainage purposes, placed 
masonry lined ditches near some settlements, and 
the work was excellent; it is in as good condition 
to-day as at the date of completion, and will prob- 
ably remain so for many years to come. 

In June, 1904, about 11 00 laborers were em- 
ployed in canal work at Culebra; they lived in 
the adjacent villages, and very few isolated houses 
existed in the bush. Many of the old French 



1 8 The Control of Mosquitoes 

buildings were occupied by laborers who had re- 
mained after the financial failure of the French 
company. 

Malarial fever was prevalent among these people, 
and they had neither the knowledge nor the means 
to combat it. At Paraiso, in September, 1904, 
there was a population of 350 of which 42 were 
sick in bed. At Bohio, a village fifteen miles 
south of Colon, blood samples were taken from 
natives, and eighty per cent, showed malaria 
infection. But even this poor and ignorant class 
of people took steps to do the best they knew 
how; they prayed for deliverance from fever and 
shunned certain localities in which the sick-rate 
was abnormally high as compared with the pre- 
vailing high fever rate. 

At Corozal, the nearest village to Panama, only 
one house was occupied, and many colored peo- 
ple told us that "to live there is to be sick and 
die." 

The situation at Ancon Hospital was extremely 
interesting. The grounds were magnificent ; there 
were palms, beautiful crotons, and other deco- 
rative plants near the wards and on the terrace, 
but the insects, and especially the ants, destroyed 
them repeatedly. The gardeners partially over- 
came this difficulty by placing hollow earthenware 




t * 




Ant-guards : Old hospital at Ancon 



The Isthmus in 1904 19 

rings of a semi-spherical section around each 
plant. They were kept filled with water and of 
course contained many larvae of both Aedes calopus 
and Anopheles as well as algae, vegetable debris, 
etc. 

The ditches near the wards were lined with field 
stone; the spaces between the stones were rilled 
with earth and grass which retarded the current of 
water. These ditches discharged onto the grass- 
covered, clayey soils, and pools remained there, 
distributed over a large area. 

The natural topography of the hill gave a fairly 
steep slope with a more gently sloping bench below 
it. The highest part of the hill is about six hun- 
dred feet above sea level. The water absorbed by 
the upper part of the hill came to the surface at a 
lower level on a clay-like formation covered with 
grass, making the hillside resemble a bog in many 
places. The outcrop of water, which oozed 
slowly from the ground, often followed the contour 
of the hill for a considerable distance. Conse- 
quently the area immediately below that contour 
was wet almost continually. 

There was a cow pasture on the top of the hill, 
and throughout the rainy season the hoof -prints 
remained wet or full of water. Ditches of varying 
widths ran down the slope, and the water spread 



20 The Control of Mosquitoes 

over the ground and sometimes did not return to 
the lower part of the ditch. In addition, the foot 
of the hill formed the shore line of an extensive 
swamp. These adverse conditions, and wet areas 
covered with vegetation, encouraged Anopheles. 
A more prolific source would be hard to imagine. 

The number of adult Anopheles present in the 
hospital wards and buildings corresponded with 
the numerous favorable propagation areas on and 
near the hillside. At night, comfort was impos- 
sible and mosquito bars indispensable. Not a 
single building was screened. The malaria and 
yellow fever patients had been accessible to 
Anopheles and Aedes calopus, and the other patients 
were near them. The patients in wards were 
located according to nationality instead of accord- 
ing to the nature of their illness. Had it been 
intended to spread yellow fever and malaria with 
the greatest rapidity among the patients as soon 
as they arrived, no better plan could have been 
adopted. Similar conditions have existed in other 
tropical countries; in fact, were customary in past 
years. 

Before sanitary work was fairly under way, with 
one or two exceptions, the small hospital sanitary 
force was down with malaria. During the first 
year of work, all the force suffered. At one time 




A ditch at Ancon: weeds retarding water flow 



The Isthmus in 1904 21 

it became necessary for the sanitary inspectors 
to be employed all night in clerical work. The 
Anopheles were so numerous that night work had 
to be done in relays ; one set of men using fans to 
protect those working. We were two thousand 
miles from the source of supplies and had to wait 
for screening, its installation, necessary supplies, 
etc. 

When the hospital was first opened and treat- 
ment given without charge to employees, the 
native laborers who had known of the suffering 
and deaths in previous years at Ancon refused 
to go to the hospital, stating that they "preferred 
to die at home." We could readily sympathize 
with their ideas, knowing what had happened in 
the past. No attempt was made to approximate 
the number of Anopheles present. The prevailing 
species was Anopheles albimanus. Inside one of 
the buildings near the hospital, fifty-four adult 
Anopheles were noted on the upper panel of a 
screen door. 

It was desirable to know the time of the day 
or night when the Anopheles would take blood. 
In July of 1904, men were dressed in white clothing 
and dark coats and made to lie on cots in an un- 
screened ward at Ancon. They were furnished 
with pill-boxes and a clock. Each time a mos- 



22 The Control of Mosquitoes 

quito bit them, or tried to, it was captured and 
placed in a pill-box and the date and hour written 
on the box. It was found at that time that 
Anopheles in the ward attacked men at rest at all 
hours of the day, and at night they became too 
numerous to make the work pleasant. It was 
noticed that they did not bite as freely near the 
doorway, where there was more light during the 
daytime, and that they absolutely refused to fol- 
low a man out into the bright rays of the sun. 

Before anti-malaria work was begun, a prelim- 
inary survey was made and Anopheles production 
areas were found near every existing settlement, 
as well as all abandoned camps that had been 
used by the French. The greater part of these 
areas was covered with dense jungle, and their 
extent could not be at once determined. There 
were numerous seepage outcrops and their out- 
put varied according to the rainfall; and prob- 
ably the contour line of seepage varied also. 
The character of the soil was often such as to 
retain the rainfall for relatively long periods, and 
innumerable small depressions existed, which 
might produce mature pupae or not according 
to weather conditions. The survey showed that 
it would be necessary to clear off large areas of 
jungle near settlements before any effective results 




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The Isthmus in 1904 23 

could be obtained, and it was decided to begin 
work at the camps that were first to be occupied 
by the laborers and American forces. It was 
thought also that oiling of wet areas would be 
attended with less successful results than in the 
Cuban campaign, because the rainfall of the 
Isthmus was often sufficiently continuous to re- 
move all traces of oil before it had had much 
effect on the mosquito larvae. When pathways 
were cut through the jungle new mosquito pro- 
ducing areas were found. 

The statistics of the days of the French Canal 
Company are incomplete, and include only a 
portion of the deaths due to malaria, as only cases 
in hospitals, or patients able to pay for hospital 
treatment, were recorded. 

In the city of Panama, which was not so badly 
infested with Anopheles as Colon, the malaria 
sick-rate and death-rate were high. The number 
of deaths recorded as due to malarial fever was : 

Date Number of Deaths Population 
From 1884 to 1893 20,000 to 

inclusive 3504 22,000 

1885 687 20,276 

During 1906, the year of highest malaria sick- 
rate of the American period of occupation, among 



24 The Control of Mosquitoes 

21,934 malarial fever patients entering the hospi- 
tals, 195 deaths occurred, or less than one per cent, 
of the cases. It can be readily understood from 
these death-rates how prevalent infection was in 
the city of Panama before 1904. The hospital 
physicians who were at Colon and Panama previous 
to 1904 state that over seventy-five per cent, 
of all hospital patients had malaria. Of course, 
in the villages out in the Canal Zone surrounded 
by jungle, breeding places for Anopheles were 
quite numerous and close to the houses. The 
question of controlling malaria appeared at first 
sight to be utterly hopeless. The United States 
Public Health Reports describe the situation as 
follows : 

From Panama to Colon, a distance of forty-seven 
miles, along the railroad there are many villages, in 
fact almost a continuous settlement the entire dis- 
tance, the total estimated population being 15,000 
in January, 1904. The population is almost entirely 
negro and Chinese. All the villages are filthy, with- 
out regulations or restrictions, without sewers, and 
having the usual water supply of the country, viz., rain- 
water during the wet season, and water from streams 
during the dry season. No attention is paid to the 
wholesomeness of the source of the water supply. 
Mosquitoes are prevalent in all these villages, breeding 
in rainwater barrels, in the swamps, along the streams, 
and in ponds. Malaria, elephantiasis, and beriberi 



The Isthmus in 1904 25 

are always to be found, and yellow fever and smallpox 
will occur when favorable clinical material presents 
itself, unless proper precautions are taken. 

In order to obtain certain data concerning 
malaria transmission, an experimental station was 
established at Ancon, and non-immunes were 
isolated there for the experiments, but so many 
Anopheles al imanus were present that it was 
extremely difficult to prevent natural malaria 
transmission. 

Low lying flat areas occurred for a distance of 
six miles inland from the Pacific terminal and to 
a still greater distance from the Atlantic Coast. 
Much of this area was affected by the highest 
tides, and Anopheles larvae were present in streams 
on steep hillsides as well as on the lowlands. 

The preliminary survey showed that Anopheles 
and other mosquitoes were present near all the 
camps, but the impassable jungle made it impos- 
sible to determine the extent of the propagation 
areas and it was evident that considerable clearing 
would have to be done to obtain the data desired. 
Innumerable small puddles were everywhere, and 
their possibilities as mosquito producers depended 
upon the frequency of the successive showers. The 
rapidity of growth of vegetation was remarkable, 
and showed that its control would be an important 



26 The Control of Mosquitoes 

factor in the anti-malaria campaign. Algae that 
protected the larvae from their natural enemies 
was often found and appeared to develop in a 
few day's time. It was evident that work would 
have to be done on an extensive scale and that 
the climatic conditions would make the campaign 
a strenuous one. One apparently discouraging 
feature was the frequent occurrence of showers that 
removed oil applied to breeding areas before it 
could accomplish its purpose. 



CHAPTER III 

METEOROLOGICAL AND TOPOGRAPHICAL CONDITIONS. 

TOPOGRAPHICAL CHANGES AND THEIR BEARING 

ON ISTHMIAN ANOPHELES 

T^HE Isthmian Canal Zone has a tropical climate, 
* high humidity, heavy rainfall, and a short 
dry season of four months or less. The continental 
divide occurs at Culebra about twelve miles from 
the Pacific canal terminal. North of Culebra all 
drainage goes to the Atlantic Ocean through the 
Chagres Valley. The attached Table No. i de- 
scribing the air temperature for 191 2 shows the sea- 
sonal variation to be very slight, with no excessive 
heat, and no marked difference of temperature at 
different points in the Zone. It always remains 
within limits that are favorable to the development 
of mosquito life. 

The yearly rainfall is not equal in all parts of 
the Canal Zone. The extremes are noted at Colon 
and Panama. On lands adjacent to the Pacific 

coast, near the city of Panama, the precipitation 

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29 



30 The Control of Mosquitoes 

is from seventy to eighty inches per year. Toward 
the divide the rainfall increases, and between 
Culebra and Colon is very heavy, increasing as the 
Atlantic coast is approached. The annual precip- 
itation at Colon is between 120 and 180 inches. 

The country along the line of the Canal is low 
and near tide level for a distance of six miles from 
the Pacific, and fifteen from the Atlantic ocean. 
The remainder of the country is thickly studded 
with hills and contains numerous springs, seepage 
outcrops, swamps, and streams. The Canal ap- 
proximately follows the line of the Chagres River as 
far as the divide at Culebra Cut, and then down 
the valley of the Rio Grande to the Pacific. There 
is very little porous soil on the Isthmus, and a large 
part of the surface soil is of a claylike character 
and is so densely clothed with luxuriant vegetation 
that travel is impossible except along the trails, 
which if not constantly used soon become over- 
grown and disappear. The lands immediately 
adjacent to the Canal produce more mosquitoes 
than places a mile or more east and west of it. 
There are extensive areas toward the Canal Zone 
boundary line and in the Republic of Panama 
in which Anopheles do not -exist. 

The meteorological tables, on the pages pre- 
viously referred to, show the large percentage of 



Table "No. 2. — Monthly rainfall by sections, Canal Zone — Year 1912 and averages. 

(Values in Inches.) 



Month. ^ 


Pacific section. 


Central section. 


Atlantic section. 


1912 


Average. 


1912 


Average. 


1912 


Average. 




0.01 
.23 
.01 
3.52 
8.39 
7.10 
9.81 
9.43 
11.74 
13.80 
7.97 
4.58 


1.30 
.97 
.66 
3.55 
9.37 
9.32 
9.48 
8.70 
9.08 
11.82 
10.78 
6.33 


0.44 
1.10 
.09 
1.51 
9.45 
11.65 
11.11 
12.45 
12.16 
14.81 
11.03 
3.88 


1.62 
1.69 
1.21 
3.65 
12.29 
10.99 
11.22 
11.89 
11.37 
13.99 
15.64 
7.90 


0.62 
2.02 
.58 
1.58 
13.49 
17.34 
16.51 
12.60 
11.05 
16.79 
22.17 
10.61 


4.79 




2.68 




2.64 




4.46 


May 


14.11 




15.14 


July 


16.31 




15.42 




11.86 




14.34 




24.64 




15.66 






Year 


76.58 


81.36 


89.68 


103.36 


125.36 


141.94 







Note.— Means are based on the records from 5 stations in the Pacific section, 11 in the Central section, 
. and 4 in the Atlantic section. All available records are used in computing averages. 

Table No. 3. — Maximum rainfall in Canal Zone Oct. 1, 1905, to June SO, 1913. 







Maximum rainfal 


. 


Stations. 


5 minutes. 


1 hour. 


24 hours.' 




Inches. 


^ Date. 


Inches. 


Date. 


Inches. 


Date. 




0.64 


Aug. 7,1908 


3.98 


Oct. 9,1911 


7.23 


May 12-13, 1912. 


Balboa (June 10, 1906) 


.90 


May 12,1912 


5.80 


June 2, 1906 


7.57 


Nov. 16-17, 1906. 


Pedro Miguel (Jan. 1, 1908). 
Rio Grande (Dec. 29, 1905). 

Culebra (July 1, 1906) 

Empire (July 18, 1906) 


.60 


Nov. 11,1908 


3.30 


Aug. 27,1908 


4.56 


Sept. 30-Oct. 1,1909. 


.75 


July 24,1908 


3.10 


Sept. 21,1912 


6.00 


Dec. 2-3, 1906. 


.64 


May 2, 1908 


3.69 


Oct. 16,1907 


5.55 


Dec. 3, 1906.* 


.60 


July 25,1906 


3.63 


Oct. 1,1909 


6.15 


Do. 


Gamboa (Nov. 18, 1005)... 


.59 


July 27,1908 


3.32 


May 11,1911 


6.56 


Dec. 2-3, 1906. 


Alhajuela (Mar. 31, 1907).. 


.60 


July 20,1909 


3.40 


Dec. 28,1909 


8.19 


Dec. 3, 1906.* 


Oatun (Aug. 24, 1907) 


.62 


Aug. 3,1912 


3.82 


May 26,1910 


10.48 


Do. 


Colon (Oct. 1, 1905) 


.64 


Aug. 25,1909 


4.90 


Oct. 8, 1909 


8.53 


Dec. 2-3, 1906. 


Porto Bello (May 1, 1908). 


»2.48 


Nov. 29,1911 


4.53 


Nov. 29,1911 


10.86 


Dec. 2S-29, 1909. 



l Maximum fall in any 24 consecutive hours. 

» No automatic record on this date; total for 24 hours ending at noon. 
* Approximate; automatic record indistinct, due to unusually excessive rate of fall. 
Note.— Dates in parentheses opposite station names refer to installation of automatic rainfall registers. 

Table No. 4. — Hourly distribution of rainfall in Canal Zone, year 1912. 
[Values in inches.] 





Total 
annual 
rainfall. 


Rainfall during 
working hours, 7 

a. m. to 5 p. m. 




Hourly rainfall. 




Station. 


Maximum. 


M1"ftn 


um. 




Amount. 


Percent 
of total. 


Hour of 
maximum. 


Accumu- 
lated 
amount. 


Hour of 

minimum. 


Accumu- 
lated 
amount. 


An con 


71.78 
71.89 
75.71 
75.14 

78.99 
89.07 
83.73 
111.83 
117.59 
147. 61 


45.37 
44.34 
57.95 
63.13 

43.45 
68.14 
65.70 
48.28 
44.26 
72.58 


63 

62 
77 
71 

55 

77 
78 
43 
38 
49 


2-3 p.m... 
2-3 p.m... 
2-3 p.m... 
2-3 p.m... 

2-3 p.m... 
3-4p.ro... 
2-3 p.m... 
3-4 p.m... 
5-6 a. m . . . 
2-3 p.m... 


10.27 
10.69 
14.88 
15.15 

14.51 
16.20 
15.44 
8.50 
8.25 
12.51 


l-2a.m... 
1-2 a.m... 
2-3 a.m... 
4-6 a. m., 

and 11 p. 

m. 
11p.m.... 
10-11 p.m. 
l-2a.m... 
9-10 a.m.. 
8-9 p.m... 
6-7 p. m. . . 


0.32 


Balboa 


.29 




.16 




.28 
.27 






.27 




.34 


Gatun 


2.56 


Colon 


1 91 


Porto Bello 


2.65 







3i 



32 The Control of Mosquitoes 

rainy days that occur each year, and particularly 
during certain months. At Panama from July to 



Table No. 5. — Monthly meteorological data — Ancon, Canal Zone, year 191$. 



Month. 



Atmospheric 
pressure 
(inches). 



Air temperature (degrees Fahrenheit). 



cS'O i 



5u 
«3 






a 



January... 
February. . 

March 

April 

May 

June 

July 

August 

September. 

October 

November. 
December. 

Year. 



29.742 
29.762 
29.749 
29. 770 
29.732 
29.742 
29.728 
29.728 
29.726 
29.735 
29.736 
29.722 



29.838 
29.858 
29.844 
29.865 
29.828 
29.837 
29.823 
29.824 
29.822 
29.830 
29.831 
29.818 



80.6 
81.3 
83.0 
82.1 
82.0 
80.8 
80.6 
80.2 
79.4 
79.0 
79.0 
80.8 



29.739 



29.835 



D.7 



*7 89.3 



63 



73.1 



Month. 



Precipitation (inches) 



Wind. 



fl l 



Maximum veloc- 
ity. 



Number of days. 



January... 
February. . 

March 

April 

May 

June 

July 

August 

September. 
October.... 
November. 
December. 

Year 



T. 

0.08 
.01 

2.68 
10.71 

5.80 
10.25 

6.33 

8.38 
17.89 

6.38 

3.27 



1.02 
.86 
.78 
2.76 
8.98 
8.15 
8.16 
7.53 
7.46 
10.92 
10.45 
4.18 



8,564 
7,705 
8,965 
6,390 
4,999 
4,118 
5,176 
5,024 
4,451 
4,538 
5,105 
5,007 



71.78 



71.25 



153 70,042 



NW. 
NW. 

NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 



NW. 34 



NW. 
NW. 
NW. 

N. 
NW. 

S. 
BE. 

N. 
NE. 

8. 
NW. 
NW. 



•15 



42 1S4 140 125 



3.8 
6.1 
5.6 
5.1 
7.7 
7.4 
7.8 
7.3 
7.6 
7.5 
6.9 
5.8 



6.6 



1 Elevation of barometer 92 feet above sea level. 
* Average for 14 years' record, 
s Tenths of sky. 



♦April. 
* February, 
sjune. 



November, 191 2, inclusive, twenty or more rainy 
days occurred each month. At Culebra, from nine- 
teen to twenty-four, and at Colon from twenty 



Conditions 



33 



to twenty-seven. These conditions favored rapid 
development of vegetation and kept in existence 



Table No. 6. — Monthly meteorological data — Culebra, Canal Zone, year 191t. 



Month. 



Atmospheric 
pressure 
(inches). 



CO 



Air temperature (degrees Fahrenheit). 



■i I, 



9 t 



i* 



3* 



January... 
February. . 

March 

April 

May 

June 

July 

August 

September. 
October... 
November. 
December. 

Year, 



29.438 
29.460 
29.442 
29.464 
29.430 
29.436 
29.420 
29.423 
29.422 
29.430 
29.428 
29.414 



29.851 
29.874 
29.854 
29.874 
29.840 
29.848 
29.832 
29.836 
29.834 
29.844 
29.842 
29.828 



79.0 
79.2 
80.4 
81.4 
81.2 
80.2 
79.8 
79.5, 
78.7 
78.6 
78.0 
78.8 



29.434 



29.846 



79.6 



96 



«5 87.2 



65 



62 



72.1 27 73.2 



72.1 



85 
84 
79 
79 
87 
92 
92 
92 
93 
93 
93 
91 



88.3 





Precipitation (inches). 


Wind. 


Number of days. 




Month. 


a 

3 

3 
g 


O 

55 


i 

•3 


S 

i. 

II 

a 

o 


a 
•a 

bog 

3 33 

St 

eg 

i 


Maximum veloc- 
ity. 


i 


•a 
§ 

a 


>> 

•o 

3 
O 


3 

A 


i 




3 

P. . 

j! 




>> 

0) 

p 




o 

§ 

> 

< 




0.05 
.33 
.02 
3.14 
8.15 
7.57 
10.12 
12.88 
14.12 
10.15 
7.59 
4.87 


1.75 
.56 
.68 

3.80 
11.16 

8.86 

9.52 
10.58 
11.23 
11.54 
12.30 

7.68 


2 
4 

1 

4 
15 
21 
22 
19 
20 
25 
24 
15 


7,697 
7,864 
8,893 
7,059 
5,538 
3,715 
4,962 
4,592 
3,975 
3,505 
5,039 
5,567 


NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 
NW. 

NW. 


28 
30 
35 
30 
27 
25 
36 
33 
32 
21 
27 
24 


NW. 
NW. 

N. 

N. 
SW. 
6E. 
NE. 
NE. 
NE. 

N. 
NW. 

N. 

NE. 


31 
24 
4 

25 

8 

15 

30 

12 

23 

7 

17 

9 


17 
9 
9 
6 



2 
1 


6 


14 

20 
22 
21 
11 

9 
13 
12 
10 

9 
16 
20 





3 

20 
21 
18 
17 
19 
22 
15 
5 





2 
15 
21 
14 
23 
22 
22 
11 
7 


3 5 




4.3 
4.1 




4.9 


May 


7.4 




7.8 


July 


7.7 




7.3 




7.5 
7.6 




7.4 
5.2 


Year .. 


78.99 


89.66 


172 


68,406 


36 


«30 


50 


176 


140 


137 


6.2 



1 Elevation of barometer 404 feet above sea level. 
* Average for 22 years' record, 
i Tenths of sky. 



«May. 
6 February. 
•July. 



innumerable small collections of water which could 
not evaporate before being replenished. The con- 
tinuity of the rainy periods, rather than the total 



34 The Control of Mosquitoes 

volume of rainfall, is the important factor affect- 
ing Anopheles propagation. 

Table No. 7. — Monthly meteorological data — Colon, Republic of Panama, year l9Jt> 



Month. 



Atmospheric 
pressure 
(inches). 



Air temperature (degrees Fahrenheit ). 



si 



B . 

as 



SB 






2^ 

P 

ia 

3 



Sx. 

3 w 



January 

February 

March 

April 

May 

June 

July 

August 

September. . . 

October 

November.... 
December.... 

Year... 



29.862 
29.880 
29.870 
29.886 
29.844 
29.849 
29.841 
29.836 
29.829 
29.834 
29.840 
29.834 



29.872 
29.892 
29.882 
29.897 
29.854 
29.860 
29.852 
29. 846 
29.840 
29.846 
29.850 
29.845 



82.2 
80.8 
82.4 
82.8 
82.0 
80.2 
80.6 
80.2 
79.4 
79.0 
78.6 
80.4 



29.850 



29.861 



80.7 



«5 84.9 



71 »10 76.5 



75.8 74.2 84.3. 



Month. 



Precipitation (inches) 



Wind. 



S 



Ph 



Maximum veloc- 
ity. 



Number of days. 



January... 
February.. 

March 

April 

May 

June 

July 

August 

September. 
October... 
November. 
December. 

Year 



0.28 
1.81 
0.66 
0.75 
12.03 
15.90 
13.13 
9.87 
12.23 
17.65 
21.81 
11.47 



3.96 

1.47 

1.67 

4.08 

12.41 

13.35 

16.38 

15.01 

12.53 

14.29 

21.86 

12.31 



10,772 
10,066 
12,550 
10,620 
7,614 
5,165 
7,574 
6,892 
5,473 
5,490 
7,519 
8,992 



N. 

N. 

N. 

N. 

N. 

W. 

N. 

N. 
SE. 
SE. 

W. 
NE. 



NE. 

N. 
NE. 
NE. 
NE. 
NE. 
NE. 

W. 

w. 

sw. 

NW. 
NE. 



117.59 



129.32 



224 98,727 



N. 



38 SW. «23 



183 122 101 



4.9 
5.5 
4.4 

3.7 
6.6 
7.3 
7.1 
6.8 
7.0 
7.5 
8.4 
5.3 



6.2 



* Elevation of barometer 10 feet above sea level. 

* Average for 42 years' record. 

* Tenths of sky. 



<May. 

* February. 

• October. , 



The Isthmus, as may be seen by reference to the 
map of the Canal Zone, is well supplied with 
streams and natural watercourses. Some of them 



Conditions 



35 



are of great length. At Gatun many flow from 
the hills toward the settled area. During many- 
rainy periods, when all the soil is well water- 
soaked, the hillside streams give least trouble, as 
the larvae are washed out of them. Unfortunately 



Table No 


. 8. — Comparative wind records — 


Ancon and Sosa, fiscal year 1912-1S. 




An con. 


Son. 


Excess 
wind 
move- 


Month. 


Aver- 
age 
hourly 
wind 
move- 
ment. 


Per 

cent 
NW. 
wind. 


Maximum velocity. 


Aver- 
age 
hourly 
wind 
move- 
ment. 


Per 

cent 
NW. 
wind. 


Maximum velocity. 




Miles 
per 
hour. 


Direc- 
tion. 


Day. 


Miles 
per 
hour. 


Direc- 
tion. 


Day. 


(per 
cent).* 


1912. 
July 


7.0 
6.8 
6.2 
6.1 
7.1 
6.7 

7.3 
9.3 
10.6 
9.7 
6.7 
5.5 


70 

55 
48 
37 
47 
£8 

64 
68 
77 
69 
63 
43 


24 
24 
31 
23 
25 
20 

2L 

26 
26 
24 
20 
32 


SE. 

N. 
NE. 

S. 
NW. 
NW. 

N. 
N. 
NW. 
N. 
N. 
S. 

S. 


14 
18 
23 
28 
17 
16 

29 
10 
23 
2 
1 
11 


10.5 
9.9 
8.9 
7.6 
9.7 
9.8 

10.7 
13.3 
15.6 
13.5 
9.4 
8.0 


90 
76 
71 
59 
66 
88 

89 
94 
96 
88 
79 
61 


44 

40 
39 
28 
36 
27 

30 

36 
36 
36 
34 
48 


SE. 
NE. 
SE. 
NW. 
NW. 
NW. 

NW. 
NW. 
NW. 
NW. 
NW. 
S. 

S. 


14 
23 
14 
22 
17 
16 

7 
17 
23 
5 
1 
11 


50 




46 


1913. 


44 

25 
37 
46 

45 
44 

47 


April 


40 


May 


40 




45 






Year 


7.4 


58 


32 


»11 


10.6 


80 


4S 


»11 


43 



i Sosa records compared with Ancon. 



* June. 



Note.— Elevation of Ancon anemometer 69 feet above ground and approximately 160 feet above meaa 
eealevel. Soaa anemometer 25 feet abovo ground, and approximately 220 feet above mean sea level. 

these hillside streams are often transporters of 
larvae and pupae, and become an important source 
of mosquitoes when they reach a lower grade, or 
enter larger streams or rivers near a settlement. 

During dry periods streams become prolific 
sources of mosquitoes; and even after the stream 
becomes dry many depressions still contain water 
in which larvae rapidly develop. As the rain- 
fall is heavy, there is a rapid run off, and erosion 



36 The Control of Mosquitoes 

and the formation of pot-holes frequently result, 
often making it difficult to keep a stream properly 
trained, and unless controlled, larvae will be found 
at its edges where there is least current velocity. 
Where branch streams occur, debris, sand, etc., are 
deposited at their junction with the main stream, 

Table No. 9. — Monthly evaporation — Canal Zone, years 1912, 1913, and averages. 

(Value In inches.) 





Ancon. 


Rio Grande. 


Gatun. 


Brazos Brook. 


Month. 


1912 


1913 


Aver- 
age. 


1912 


1013 


Aver- 
age. 


1912 


1913 


Aver- 
age. 


1912 


1913 


Aver- 
age. 


January 

February.. 

April . , . 
May 

July !. 

August 

September. 

October 

November . 
December.. 


7.370 
6.755 
7.795 
5.721 
3.746 
3.098 
3.386 
3.648 
3.395 
3.458 
3.723 
5.333 


5.935 
6.439 
7.816 
6. 465 
3.963 
3.615 


4.889 
5.384 
6.480 
4.813 
3.149 
2.708 
3.018 
3.021 
3.120 
3.314 
2.956 
4.025 


6.363 
6.134 
77.099 
6.732 
5.350 
3.836 
3.908 
3.983 
3.335 
3. 703 
3.275 
4.723 


5.392 
5.844 
6.762 
6.436 
4.033 
3.812 


5.577 
5.605 
6.832 
5.454 
4.372 
3.388 
3.715 
3.749 
3.739 
3.590 
3. C10 
4.120 


7.208 
6.048 
7.649 
7.394 
5.335 
3.263 
3.889 
4.316 
3.799 
4.123 
3.351 
4.809 


5.435 
6.889 
8.602 
7.333 
4.606 
5.083 


6.322 
6.468 
8.126 
7.304 
4.970 
3.031 
4.224 
4.362 
4.191 
3.806 
3.016 
5.092 


6.006 
5.672 
7.081 
7.321 
5.707 
3.729 
4.425 
4.011 
4.487 
3.970 
3.100 
4.860 


6.387 
6.616 
8.455 
7.406 
4.107 
4.500 


5.842 
5.493 
7.140 
5.663 
4.474 
3.492 
3.710 
3.906 
4.140 
4.063 
2.834 
3.790 


Year. 
Daily mean 


57.428 
.157 




46.877 
.128 


58.501 
.100 




53.137 
.146 


61.184 
.167 




01.032 
.107 


60.929 
.166 




54.547 
.149 



Nora.— Averages at Rio Grando and Brazos Brook are based on four years' record; Ancon fivo years' 
record; and Gatun two years' record. 

Evaporation measurements are from floating pans 4 feet in diameter and 10 inches deep at Rio Grande, 
Gatun and Brazos Brook, and insulated tank 10 inchos in diameter at Ancon. 

For monthly evaporation during past years, see previous annual reports. 

and afford collecting places for larvae brought 
down-stream. 

Various accumulations of vegetable matter, 
twigs, branches, etc., are found at the edges of 
rivers and make suitable hiding places, often 
inaccessible to the fish that prey upon mosquito 
larvae. At some points, seepage outcrops occur 
on the stream banks and are constant sources of 
larvae throughout the year. It was not at all 



Conditions 



37 



unusual for the water in a stream to disappear 
into the substrata during the dry season and 
reappear at a lower level. As the areas so affected 
vary from year to year, it was necessary to inspect 
the stream beds up to their sources. There are 




RAINFALL CHART 

many marshy areas of large extent within fifteen 
miles from the Atlantic and six miles from the 
Pacific, in addition to the inland marshes near the 
occupied camps. 

There is much marshy hillside caused by seepage 
outcrops. The impervious character of the soil 
enables small depressions to hold water for rela- 
tively long periods, especially where rank vegeta- 
tion proves a barrier to evaporation by sun and 



38 The Control of Mosquitoes 

wind. The rainfall tables show the number of days 
a month on which rain fell. The depressions 
referred to above take time to dry out, and mud 
contains sufficient moisture to maintain life in 
larvae of Anopheles and other mosquitoes. Admit- 
ting that the Anopheles albimanus readily travels 
half a mile or more, the numerous small depres- 
sions hidden by vegetation within a circle of half 
a mile radius are of importance, especially during 
very wet periods. 

The climatic conditions of the Isthmus, except 
during the brief period of a few weeks toward the 
end of the dry season, are ideal for the propagation 
and multiplication of Anopheles. It is difficult to 
conceive of a locality where topographical changes 
have been made more frequently and rapidly. 
The cost of anti-malaria work depends largely upon 
topographical and climatic conditions. 

Many miles of temporary track were frequently 
changed and often each tie removed left a water- 
holding depression. The excavation and trans- 
portation of material excavated was continuous 
for ten years. As the depth increased, more 
water seeped into the new channels or benches 
being cut by the steam shovels, and the former 
ditch sites were excavated. 

As the bottom of the Canal was lower than the 




A topographic change : near Empire 




Constantly changing topography: near Miraflores 



Conditions 39 

surrounding country most of the sub-surface 
water went toward it. The dumps where the 
excavated material was "wasted" often blocked 
natural drainage channels and ditches. Water 
collected constantly and proposed excavations and 
fills interfered with or prevented permanent drain- 
age schemes. As the Canal neared completion, 
the bottom became too flat to drain economically 
and numerous small pools were left. Hundreds 
of acres of this territory had to be inspected 
and oiled each week. The hilltop of to-day be- 
comes a depression a month later, and permanent 
drainage is often out of the question. The history 
of tropical malaria is generally alike east or west. 
It develops most rapidly when the soil is dis- 
turbed by large and extensive excavations and 
fills accompanied by the introduction of non- 
immune labor housed near the site of their 
work. Until now, no precautions had ever 
been taken in similar construction work in 
the tropics to prevent an increase in the num- 
ber of places suitable for the development of 
malaria-conveying mosquitoes. Pools and stag- 
nant water were brought into existence by fills 
that had settled. By the time the surface of 
a dump was in condition to hold water it was 
covered with rank vegetation, often more than 



40 The Control of Mosquitoes 

six or eight feet high, and the pools formed 
were hidden. 

If inadequate provision is made for taking care 
of natural watercourses blocked by uninterested 
engineers, acres upon acres of new swamp lands 
may be formed, which are often ideal breed- 
ing grounds for mosquitoes. They contain few 
aquatic enemies of mosquito larvae, plenty of 
food supply, and the tangle of vegetable growth 
protects the eggs and furnishes hiding-places for 
larvae and pupae. Such places are ideal for mos- 
quitoes as soon as made, and outrival the freshly 
dug excavation, which is not frequently used by the 
Anopheles for ovipositing until conditions, such as 
protection for the young, food supply, and vege- 
table matter, tempt their presence. 

It can be readily understood that if the area at 
the rear of the new dump or blocked portion of the 
drainage channel is flat or gently sloping toward 
the dam, a much larger area containing vegetation 
will become flooded. If the final water surface 
does not rise above the vegetation, the mosquitoes 
are better pleased. In many cases, nature lends a 
helping hand, and the vegetation under the water 
grows rapidly until it reaches and extends beyond 
the surface. Under these conditions, aquatic 
plants develop and fish find the larvae with diffi- 




Daily change of topography 



I 



Conditions 41 

culty and remove few of them. The water-fowl 
appear and may be the cause of the introduction 
of the kind of fish they come to catch. It is not 
at all improbable that fish-eggs stick to their legs 
and are thus transported from one place to another. 
Extensive construction work, as a rule, is per- 
formed by contract. Each of the contractor's su- 
perintendents is responsible for one particular 
phase of the work and his entire time and attention 
are devoted to it. The foreman on the dump must 
unload his cars and return them within a minimum 
of time, the tracks must be moved with equal 
rapidity. If a culvert is to be elongated and no 
pipe is available, some makeshift is used and prob- 
ably no attention is given to grade when the pipe 
is laid. The work is performed in record time, or 
possibly a record is broken, and the cost of the 
work for that day, week, or month is reduced an 
appreciable amount. Probably such saving and 
efficiency are properly rewarded, and the increased 
salary or bonus acts as a spur to even more rapid 
work. The makeshift culvert is soon covered up 
and does not show. If it collapses some time after- 
wards, the cause of the collapse is unknown. A 
lagoon is formed at the back of the dam. Unless 
the entire valley is filled, the artificial mosquito- 
producing area created is permanent, and when 



42 The Control of Mosquitoes 

the country becomes settled those living within a 
half-mile or so will be malarial, and people passing 
through the district will be affected similarly. 

It is not an economy to expedite construction in 
such a manner. If a contract takes a long time to 
execute and the laborers become infected by 
Anopheles, created by the foreman's energetic 
though short-sighted action, what of the reduced 
energy or vital force of the workmen? Labor 
receives a daily wage and any decrease of output 
increases the cost of supervision. How does 
the loss of the laborers' efficiency compare with the 
saving made by .neglecting proper care of the 
natural watercourse? If all, or a large part, of 
the force becomes infected what is the contractor's 
monetary loss? 

History shows that important contracts have 
failed in the tropics, and in some cases the entire 
project has had to be abandoned. The anti- 
malaria campaign on the Isthmus showed exactly 
how and why these failures happen, and also pro- 
vided opportunity for the study that may assist 
in determining the best and most economical 
means of overcoming future difficulties of similar 
or related character. 




Blocked watercourse changed into an Anopheles breeding-place 



CHAPTER IV 

THE SPECIES OF ANOPHELES ON THE ISTHMUS 

A T the beginning of the Isthmian anti-malaria 
*** campaign available knowledge on this sub- 
ject was very limited, and confined largely to the 
experience gained in Cuba. It was not known how 
many different species of Anopheles existed, nor 
was it definitely known which of them were the 
important malaria carriers. The preliminary in- 
vestigations demonstrated that they were not of 
domestic habits similar to the Aedes calopus and 
could not be considered house mosquitoes. Nu- 
merous containers near dwellings were carefully 
examined for Anopheles larvae but none were dis- 
covered. The propagation areas appeared to be 
limited to seepage outcrops, pools, ponds, lagoons, 
ditches, streams, and the edges of rivers. 

It was not thought that the daily flight range 
was extensive, nor was any information available 
on this subject with respect to the different species. 
It was easy to see that rank vegetation served as a 

43 



44 The Control of Mosquitoes 

shelter or harboring place for Anopheles during the 
daytime, as well as for other mosquitoes. The 
climatic conditions were so different from those 
previously encountered that it was evident much 
investigation or pioneer work was required to ob- 
tain data pertaining to the general life history 
and habits of Isthmian Anopheles. We had no 
means of determining how seasonal changes would 
affect propagation, and the available data were 
unreliable. It was generally believed at that time 
that all mosquitoes traveled more or less with 
gentle air currents, but there was no positive 
knowledge of the habits of flight, and the length 
of flight of Anopheles, or of any other Isthmian 
mosquito. This was yet to be determined. It 
was not known if or how topography affected the 
distribution of species, whether Anopheles larvae 
thriving in small collections of water held by plants 
were of economic importance, or whether certain 
species were confined by fixed geographical limits. 

Dr. O. L. Howard assisted in the work in many 
ways and furnished valuable suggestions and 
advice. 

Important collections of available species of 
Zone mosquitoes were made by Mr. A. Busckof 
the Smithsonian Institute and by Mr. A. H. 
Jennings, entomologist of the Isthmian Sanitary 



Species of Anopheles 45 

Department. The determination of species found 
was made by Mr. F. Knab. Detailed studies 
of the relation to malaria of Isthmian Anopheles 
were made by Dr. S. T. Darling, z and portions of 
his published work are quoted. 

In order to have sufficient adults for the experi- 
mental work, the sanitary inspectors along the line 
of the Canal sent pupae and well developed larvae 
to the laboratory daily. Anopheles larvae and 
pupae are delicate organisms and must not be 
subjected to rough treatment. They were trans- 
ported in wide-mouthed jars, not too many in a 
jar, containing about an inch of water and shaded 
from the sun. If several inches of water are placed 
in the temporary container and subjected to the 
direct rays of the sun, or if the larvae are too much 
overcrowded and subjected to constant shaking, 
many will die. By having shallow water but slight 
effort is needed for the larvae to reach the surface. 
In collecting larvae in the field white enameled 
saucers or dippers were found convenient, as the 
larvae are easily visible against a white back- 
ground. 

In connection with the experimental work con- 
ducted at the laboratory, it became necessary to 
collect live adult Anopheles from houses at the 

1 See his Studies in Relation to Malaria. 



46 The Control of Mosquitoes 

various villages, ship them across the Isthmus, and 
have them arrive in their normal healthy condi- 
tion. It was found absolutely essential to keep 
them shaded from sunlight, rain, and strong air 
currents. They appear to die rapidly if placed in a 
drying wind, which apparently causes evaporation 
that is fatal to them. The adults die if left 
overnight in mosquito-bars out in the open. If 
transported in cages few will die if the cage is 
completely covered with paper. 

In the biting experiments made by Dr. Darling 
to determine which of the Isthmian Anopheles 
were malaria carriers, seventy per cent, of the Ano- 
pheles albimanus used became infected, about sixty 
per cent, of the Anopheles tarsimaculata, and thir- 
teen per cent, of the Anopheles pseudopunctipennis . 
No Anopheles malefactor became infected although 
several bit the same person who infected the Ano- 
pheles albimanus. The conclusions drawn were: 
that Anopheles albimanus was the all-important 
transmitter of malaria fever in the Canal Zone at 
the time the experiments were made. Anopheles 
tarsimaculata was probably as susceptible to in- 
fection as Anopheles albimanus. The former, 
however, had a much more limited geographical 
distribution at that time, and appeared to be 
numerous only near Colon on the Atlantic coast. 



Species of Anopheles 47 

Anopheles pseudopunctipennis appeared to be 
only slightly concerned in the transmission of 
malarial fever, if at all, as only about twelve per 
cent, of the specimens used became infected under 
the most favorable artificial conditions. 

Anopheles malefactor did not become infected. 

It also appeared in some cases that even the sus- 
ceptible mosquitoes possessed immunity toward 
the malaria parasite and failed to become infected. 

Unfortunately, Anopheles albimanus is the most 
abundant of the Isthmian Anopheles, and it makes 
stronger efforts to obtain entrance into inhabited 
buildings than any other species. It seems to 
prefer breeding places exposed well to the sun, and 
the green algae in such exposed collections of water 
provides food for its larvae. The larvae are found 
in stagnant water but not when heavily charged 
with sewage; and at the edges of streams and 
rivers in places where there is practically no cur- 
rent. Although they are found at the surface in 
deep bodies of water when plenty of aquatic vege- 
tation, debris, or other forms of protection are pre- 
sent, yet they are frequently found in puddles 
having a depth of only a fraction of an inch. 
Even after the water disappears the larvae often 
continue to live for some time under a layer of 
algae or in the soft mud. The adult will fly a long 



48 The Control of Mosquitoes 

distance to reach occupied houses; but is seldom 
found in vacant buildings. 

The Anopheles pseudopunctipennis is found 
throughout the Isthmus, is not as strong a trav- 
eler as the other carriers, and is not so commonly 
found in houses as Anopheles albimanus or Anoph- 
eles tarsimaculata. Its season of abundance ap- 
pears to be more limited. Running water that 
is relatively clear seems to appeal to this species. 
It does not bite as persistently as the others, and 
its relation to malaria on the Isthmus is not con- 
sidered important. 

Anopheles malefactor is apparently a non-carrier 
but a vigorous biter. At times large numbers 
of this species are found in houses. It recently 
became the most numerous species at the huts 
along the shore of Gatun Lake, when the water ele- 
vation reached eighty feet above sea level. Several 
months later it became relatively scarce. 

The other species of Anopheles are not commonly 
found in buildings, and so far as malarial fever 
transmission is concerned are not of economic 
importance. Regarding the identification of lar- 
vae, Dr. Darling has supplied the following data: 

I have made no attempt to determine in detail all 
the anatomical characteristics of anopheline larvae 
of this region; that has been done for some species by 




Aquatic vegetation sheltering larvse 




Aquatic vegetation sheltering larvae 



Species of Anopheles 49 

Knab. The chief differentiating larval characters of 
the common anophelines of this region are these: 

A. albimanus or white-footed group: 

Palmate hairs on all abdominal segments and some- 
times on postero-external angle of the thorax. 

Antennae without a tuft of hairs. 
A. pseudopunctipennis group: 

Palmate hairs on third, fourth, fifth, sixth, and 
seventh abdominal segments, but none on the 
first and second. On the latter two, however, 
there is a rudimentary stalked tuft replacing 
the palmate hairs. 

Antennae without a tuft of hairs. 
A. malefactor or spotted-legged group: 

No palmate hairs on first and second abdominal 
segments, but palmate hairs on all remaining 
segments. 

Antennae with a tuft of hairs. 

These characters are very striking and sharply sep- 
arate the malaria transmitting A. albimanus group 
from other varieties. With care it is frequently 
possible even in muddy water, from an examination of 
the indentations of the surface film caused by the 
palmate hairs, to at once determine the presence or 
absence of members of the A. albimanus group. In 
this group there is no break in the indented film, but 
in the two other groups there is a well-defined non- 
indented break in the film, due to the lack of palmate 
hairs on the first and second abdominal segments. 

The size of the palmate hairs on the postero-lateral 
angle of the thorax, and the presence of these hairs on 
the thorax, first and second abdominal segments, is 



50 The Control of Mosquitoes 

subject to some variation. It would seem that the 
white-footed group is undergoing some variation with 
regard to the size and location of these hairs, and 
apparently they are becoming rudimentary on the 
thorax and first abdominal segment. 

The larvae are easily frightened and remain 
hidden under water during long intervals, and for 
that reason are sometimes difficult to detect. 
Experiments were made by immersing larvae in 
cages in the body of water from which they were 
taken, and it was found that some of them re- 
mained alive under water for a period of two hours, 
even though the surface of the water was covered 
with oil after the cage was immersed. 'It is not 
widely known that Anopheles rest and remain upon 
dark clothing for relatively long periods although 
the wearer may be walking rapidly. It has been 
ascertained by observation that in this manner 
people convey them into houses that have been 
properly screened. Large numbers are carried 
long distances by trains at night. One obser- 
vation was made in a case where a mosquito 
(genus unknown) resting on the shoulders of a 
man wearing a dark blue serge coat was carried 
from Colon to Porto Bello on board a steamer. 
The time of the trip was nearly three hours, and 
the distance about twenty miles. Observers were 



Species of Anopheles 51 

afraid of disturbing the specimen by close approach 
but it was not an Anopheles. 

There is no doubt at the present time that the 
Anopheles albimanus is responsible for practically 
all of the malaria transmission in the Canal Zone, 
except at Gatun and Colon, where Anopheles 
tarsimaculata sometimes exist in numbers large 
enough to be of equal economic importance. The 
decrease of malarial fever in Panama will be in 
proportion to the eradication of these two species. 

It is now known that both species travel in 
enormous numbers over long distances (if other 
suitable propagation areas are not available) 
between their place of origin and the nearby settle- 
ments. On the Isthmus, in two instances where 
breeding was prolific, they have been known 
to travel from half a mile to a mile to reach houses. 
They do not seem able to remain long in a very 
strong light, and as a rule prefer darker places. 
No other Isthmian mosquitoes are so persistent in 
attempting to enter screened houses, and yet once 
inside they seem unable to find a way out, and 
collect on the screening soon after daylight, and 
again at dusk. When they find they cannot get 
out they return to the interior of the building, but 
make another effort to pass the screened openings 
at the same hours next day. They are seldom 



52 The Control of Mosquitoes 

found on the screens between 9 a.m. and dusk. 
When Anopheles in buildings are trying to find 
openings in the screens of windows or balconies 
they are not easily frightened and are readily 
captured. They are so persistent in seeking an 
opening that it is necessary to alarm them several 
times before they will leave the screening. 

When such extensive topographical changes 
were made that it was temporarily impossible to 
control the increased influx of mosquitoes at a 
camp, the laborers of the oiling brigade destroyed 
mosquitoes found in barracks in the early 
mornings. 

A description of Isthmian Anopheles as given in 
Darling's Studies in Relation to Malaria is quoted 
below : 

The following is a list of anophelines of the Canal 
Zone: 

Anopheles argyritarsis, R. D. 
Anopheles tarsimaculata, Goeldi. 
Anopheles gorgasi, D. K. 
Anopheles albimanus, Wied. 
Anopheles cruzii, D. K. 
Anopheles apicmacula, D. K. 
Anopheles punctimacula, D. K. 
Anopheles malefactor, D. K. 
Anopheles eiseni, Coquill. 
Anopheles franciscanus, McCrack. 
Anopheles pseudopunctipennis, Theob. 




3 

O 

o 
pq 

ctS 

<D 

a 

a 
B 

CO 



Species of Anopheles 53 

The above eleven species of anophelines have been 
collected in the Canal Zone during the past eight 
years. They are not taken nor do they exist in their 
breeding places in anything like equal numbers. 
For example: Only one specimen of A . gorgasi has been 
found. Of the eleven species, the commonest ones 
are A. albimanus, A. pseudopunctipennis, and A. 
malefactor, but this again must be qualified by stat- 
ing that the predominance of a species varies from 
season to season and from place to place. In certain 
villages, upon going through the barracks only A. 
albimanus will be found, while in other villages from 
five to ten per cent, of the mosquitoes will be A. 
pseudopunctipennis, and at Ancon during October, 
1908, twenty-seven per cent, were A. malefactor and 
seventy-two per cent. A . albimanus. A . tarsimaculata 
appears to be distributed solely near the Atlantic. 
Mr. A. Busck, of the Bureau of Entomology, United 
States Department of Agriculture, who collected and 
made observations on Zone mosquitoes during 1907, 
gave it as his opinion that A . pseudopunctipennis was 
the commonest anopheline during the period of his 
stay. 

The necessities of the Canal operations in excavat- 
ing and filling change the topography of districts and 
localities so as sometimes to convert salt marshes into 
fresh- water ponds, or to make tracts of land contain- 
ing few anophelines into a vast swamp in which they 
luxuriate. On the other hand, swamps and breeding 
places may be drained or filled in the work of excava- 
tion. These factors, among others, influence the num- 
ber and variety of species in a locality. 

The commoner anophelines of the Canal Zone may 
be divided into three groups: 



54 The Control of Mosquitoes 

(A) The white hind-footed group, comprising: A, 

argyritarsis, A. albimanus, A. tarsimaculata. 

(B) The leg-uniformly-colored group, comprising: 

A. pseudopunctipennis, A. franciscanus. 

(C) The spotted-leg group, comprising: A. male- 
factor, A. apicmacula. 

These groups present well-marked differences in the 
markings of adults, in the breeding habits and ana- 
tomical characters of the larvae, and, as will be shown, 
they possess varying susceptibilities to malaria. 




The rising waters of Gatun Lake 



CHAPTER V 

ANOPHELES PROPAGATION AREAS 
WATER CONTAINERS 

HTHE larvae of Aedes calopus and Anopheles are 
** seldom found in the same water. On the 
Isthmus the larvae of the latter are seldom found in 
containers, while Aedes calopus are found only in 
containers near inhabited buildings. If containers 
are upset or their contents enter into a pond or 
ditch the larvae of Aedes calopus will develop to ma- 
turity; again, if broad flat containers are so placed 
that vegetation grows in them, or if they are covered 
up in the grass and gather vegetable matter, dead 
leaves, twigs, etc., resembling natural breeding 
places, Anopheles will at times be found in them, 
but these conditions rarely occur and are not 
of practical importance. Isthmian Anopheles are 
not container breeders, and the sum total produced 
by water containers is very small. They are 
found occasionally in large wells or cisterns where 

55 



56 The Control of Mosquitoes 

the water is near the ground surface, and into 
which dead grass, sticks, and leaves have fallen. 
The number of these collections of water is limited. 

HOOF-PRINTS 

The hoof -prints of cows and horses become 
important Anopheles producers. Riders often 
take horses over soft ground and in the wet season 
each hoof-print may become a source of larvae. 
Cows seem to be particularly fond of walking in 
soft-bottomed ditches, and remaining at the edges 
of ponds. In this climate they are not stabled. 
Where the soil of the pasture is of a soft or clayey 
character, the foot-prints may be one to six inches 
or more in depth. These depressions often hold 
water throughout the wet season, and retain 
it from showers during the dry season. It is a 
difficult and expensive task to locate and fill, or 
treat, all hoof -marks holding water in a large 
flat field. The conditions are not improved if 
such a pasture is subjected to occasional flooding. 
It has been necessary in some instances to place 
fences around ponds and portions of pasture lands 
that become prolific sources of mosquitoes. In a 
few cases, where wet pasture lands were close to 
thickly settled suburbs, or villages, it became 
necessary to have the cattle removed elsewhere. 




Cattle on low pasture lands: Panama 



Anopheles Propagation Areas 57 

In the dry season pasturage is not good on dry- 
lands, and the owners of animals are then inclined 
to turn them loose, or fasten them in low spots, 
and near ditches. An active animal can spoil a 
trained ditch in one night, and leave it in a condi- 
tion to become the most prolific source of mos- 
quitoes in the vicinity. This matter was found 
to be so important that legislation became neces- 
sary to keep ditches in proper shape. It is unlaw- 
ful now for horses or cattle to be at large, or tied 
in places where their presence interferes with 
anti- Anopheles operations and becomes a sanitary 
nuisance. Even so, it is necessary to put up sign 
boards along ditches and in places where animals 
are not desired. When sign boards were first 
placed on soft ground to notify people not to tie 
animals in that vicinity, some poor ignorant 
natives who could not read thought the sign posts 
were excellent objects to which to tie their animals. 
Night policing is still essential to enforce the 
ordinance. 

WHEEL TRACKS OF WAGONS 

On bad roads, not frequently used, the rut 
marks produce Anopheles and Culex, but where 
travel is frequent there are no larvae. Where 
wagons pass through pasture land in the wet 



58 The Control of Mosquitoes 

season and haul material over fields for construc- 
tion purposes, areas of considerable extent are cut 
up and the drivers seldom use the same route 
twice; they find hauling easier over untrodden 
ground, and temporary roadways may thus be 
widened as much as a hundred feet. Near settle- 
ments the matter is of sufficient importance to 
make the filling of these new ruts necessary. It is 
more economical to fill in than to treat with oil 
weekly for an indefinite period. 

EFFECT OF LONG RAINY PERIODS AND FLOODS 

Floods occur during the rainy season and are 
generally preceded and followed by showers; and 
the rapid currents thus caused removed many if 
not most of the larvae from the banks of rivers, 
streams, ditches, and the pools or depressions near 
them. Unfortunately the overflow reached depres- 
sions on adjacent lands and caused new temporary 
breeding places. When the flood was of short 
duration and was followed by dry weather and 
strong winds it was even advantageous. The 
latter condition rarely happened on the Isthmus. 

Continuous rainy periods with daily showers 
for twelve days or more, whether accompanied 
by floods or not, are the cause of prolific mosquito 
production on flat lands. Practically all Canal 




The effect of floods : Empire 




Algae united with oil in mat-like masses: Empire 



4 



% 



Anopheles Propagation Areas 59 

Zone land is covered with luxuriant vegetation 
which retards evaporation. On flat lands mosquito 
eggs were laid in shallow water pools or films of 
water and accumulated in the relatively low spots. 
These places were grass covered and before they 
dried sufficiently to kill off the developing larvae, 
another shower fell. If the wet mud was col- 
lected and dissolved in water, mosquito larvae in 
all stages of development were often found. In 
excessively long rainy periods it is not easy to 
locate, reach, and treat small places dispersed 
over large areas, but if they are neglected, enor- 
mous numbers of mosquitoes ensue. Evapo- 
ration and ground absorption may or may not 
dry ground sufficiently to prevent the develop- 
ment of the greater part of the mosquito crop. 
Just what will occur cannot be foreseen, nor can 
it be estimated in advance during which month 
of the rainy season such ideal mosquito conditions 
may prevail. 

A variation of rainfall at villages three miles 
apart often resulted in a large influx of adults 
in one village and not in the other. At times the 
areas apparently needing attention were so exten- 
sive that the situation appeared hopeless, but 
experience gained in each locality by the inspector 
in charge was of great value. A new man requires 



60 The Control of Mosquitoes 

time to become thoroughly acquainted with the 
conditions peculiar to his district, that each day's 
work may produce the maximum of effective 
results. In time he becomes expert in omitting 
much that is but apparently necessary. 

STREAMS 

Large and small streams and natural water- 
courses, although dry for several months of the 
year, often become important propagation areas. 
Their relative importance or output of adults 
varies with the season. As a rule, during the wet 
season larvae are found in quiet places along the 
banks where vegetation occurs or overhangs the 
banks or where debris collects. It seems to 
be an instinct of the Anopheles to lay her eggs 
where there will be a maximum of protection, or 
hiding places, and of food supply for her brood. 
Small detached bodies of water adjacent to the 
stream are favorable; and where the banks are 
muddy, the footprints of those looking for larvae 
may become filled with water by seepage from the 
stream, and later contain larvae. Where the water 
is quiet or shallow, green algae develop rapidly 
and by retarding the current assist the Anopheles. 
These places offer favorable harboring places for 
larvae. 



Anopheles Propagation Areas 61 

"Pot-holes, " or circular depressions, often form 
in the stream bed. The current may be swift only 
at the center and larvae may be present at the 
edges where the debris collects. A sharp down- 
pour will often collect most of the debris, algae, eggs, 
larvae, and pupae and carry them on downstream. 
They may, and often do, collect in quieter places 
in the larger stream or lagoon below. Where 
streams flow toward a settlement and empty into 
quieter waters near it, the adult mosquitoes in 
houses often increase suddenly, due to the new 
supply of pupae and larvae thus transported toward 
it. 

It must not be assumed that algae in ditches 
when treated with oil or larvacide will cease to 
exist. A week or less may start and complete 
a new growth. Often crude oil and algae unite 
and form a mat that floats on the surface and in 
a few days a part or all will settle to the bottom 
of the stream; or may collect in irregular depres- 
sions along the bank. Such conditions offer 
hiding places for larvae and make inspection 
both slower and more difficult. In shallow streams 
having coarse gravel or stones on the bottom and 
along the wetted perimeter, when debris, grass, or 
well-developed algae are absent, larvae hide under 
the small stones, and though none may be detected 



62 The Control of Mosquitoes 

at the water surface it is always well to remove 
sufficient stones to be sure that they are not hiding 
underneath. Frequently they remain hidden for 
long intervals. When the stone under which the 
larvae are hiding is moved, they will rapidly travel 
to the next nearest stone that affords a suitable 
hiding-place. 

As the dry season advances, the source of hill- 
side streams moves farther downhill, the upper 
part remaining dry. In case the stream bed is of 
irregular grade and contains deep depressions, 
as the bed becomes dry pools remain and become 
breeding places. Should the stream be of great 
length it is so easy to assume that its entire upper 
length is dry that such places are apt to be over- 
looked. Eventually the pools become dry, but 
generally produce one or more crops of mosquitoes 
before this happens. During the dry season, if a 
shower falls, the stream bed will probably be dry 
within a day or two, but it is never certain that 
these depressions have not collected water which 
they may retain for a week or more. 

In the upper portion of the stream bed and 
higher than its dry season source, the sub-surface 
flow may outcrop at one or more points, and, due 
to the soil formation, grade, etc., flow along the 
stream for a short distance and again disappear 




c3 
> 



&0 

u 



o 
o 



^5 



*d 
o 






Anopheles Propagation Areas 63 

into the ground. The locations of the portions of 
the stream that act in this manner may change 
from year to year, and the observer is never sure 
that a dry stream is not producing mosquito 
larvae until he has followed it throughout its 
entire length. 

A minimum of mosquito larvae will be present in 
a stream when it has been properly trained, that 
is, reduced to the minimum width of uniform cross 
section and freed from stones, grass, and debris 
that would interfere with the flow or velocity and 
furnish hiding-places for larvae. 

RIVERS 

The larger rivers, where the banks are steep, 
are not sources of larvae. As a rule they are less 
troublesome in the wet season than in the short 
dry one. If the banks are not much above the 
average water level, where flat lands are adjacent 
and floods occur, we have conditions similar to 
those in lagoons. At times of great floods, twigs, 
branches, and even whole trees are carried down- 
stream and when they come to rest may act as 
collectors and hold grass, vines, and finely divided 
debris. Such places become sources of mosquitoes 
that larvae-eating fish or top minnows often cannot 
catch. Obstructions of this nature at times change 



64 The Control of Mosquitoes 

the direction of the river bottom and leave new 
isolated pools as the water recedes. The high 
water causes much silt containing plant food to 
collect on the banks. This in turn produces 
luxuriant vegetation at the water's edge. Fre- 
quently the vegetation extends into the water 
and retards the current near the shore sufficiently 
to create suitable areas along shore in which 
Anopheles larvae accumulate and remain. The 
Rio Grande on the Pacific slope of the Isthmus 
has been expensive to control because of these 
conditions, and it has been necessary to have 
workmen in boats continually on the river for 
mosquito control. 

Rivers may or may not assist mosquito develop- 
ment in the wet season as above described. They 
are generally a most prolific source in the dry 
season. As the pools, ponds, streams, and marsh 
lands dry, the rivers become more sluggish and 
are the only available water sources remaining. 
Naturally the mosquitoes use them. Where 
the banks are kept clean, free from vegetation, 
debris, and stones in shallow water, the larvae 
are seldom found. Mosquitoes instinctively avoid 
places that fish and other enemies reach easily, and 
lay their eggs in more favorable places. They 
select shallow pools with stony bottoms in the river 




Oiling of breeding-places along a river bank 



Anopheles Propagation Areas 65 

bed. Then vegetation grows around the edges 
in shallow water giving the desired protection. 
As the water is shallow, it becomes warmer and 
this assists the rapid development of algae. 

The larvae can penetrate the algae but small 
fish cannot. Algae containing larvae may be 
detached and floated downstream. Fish swim 
to and fro around it, and follow it, trying to seize 
the larvae, but they seldom appear to succeed. 
Where the slope of the river bank is gradual, and 
the water at the edges shallow, with gravel or 
stone at the bottom, Anopheles larvae are often 
found, providing other nearby and better pro- 
tected breeding places do not exist. With the 
first heavy floods of the rainy season most of these 
river production areas are promptly eradicated. 

SEEPAGE 

Seepage water is water that flows underground 
along an impervious stratum and reaches the 
ground surface when that stratum becomes exposed 
at the surface, or approaches it. Or it may come 
through a stratum that is more or less porous and 
water bearing. The places where the water 
appears at the surface are called seepage out- 
crops. They are frequently found on benches, hill- 
sides, and in small valleys. In areas where they 



66 The Control of Mosquitoes 

are present, sharp changes of grade, such as steep 
hillsides terminating on fiat ground, or on more 
gentle slopes, should be carefully examined. 
The seepage on a hillside outcrop may approxi- 
mately follow a contour line. The escaping 
water then flows downhill, and may again be 
absorbed by the soil, or continue to flow until it 
reaches a natural drainage course, or come to rest 
in a depression and form a pool or pond. On hill- 
side seepage areas only a thin film of water is 
present, but small depressions in the ground give 
a depth of water sufficient for mosquito develop- 
ment. 

Naturally the temperature of the water is 
relatively high and frequently seepage areas con- 
tain much algae and few enemies of larvae. Cattle 
complicate the situation by leaving deep hoof- 
prints. The outcropping water may be present 
throughout the year or only during short periods. 
Each outcrop is a law unto itself. Strange as it 
may seem, some places produce more water 
immediately after the rainy season, than during it. 
One such area was discovered at Balboa at the 
foot of a hill composed largely of trap rock. 

In several localities seepage outcrops had been 
present only twice in ten years. Of course if 
such places are neglected it will be extremely 







o 

c 

Ih 

*o 

c 

ct3 



> 



Anopheles Propagation Areas 67 

difficult to account for the presence of mosquitoes> 
and more distant production areas, winds, etc., 
may wrongly be held responsible for a temporary 
influx. Seepage may be found at most unexpected 
places during or after long rainy periods ; it almost 
invariably produces mosquitoes, and in many 
cases may not be noticed until some adults have 
been produced. Nearly all seepage outcrops as 
well as areas flooded by seepage water were covered 
by the same class of vegetation that grew above 
the outcrop, and there was nothing to denote their 
presence. One cannot appreciate the number of 
mosquitoes produced by even small seepage out- 
crops without actually inspecting them. 

LAGOONS, LAKES, PONDS, ETC. 

Many parts of lagoons in the tropics are impass- 
able and trochas or paths have to be cut through 
the heavy growth to penetrate some parts of them. 
Examination, or mosquito inspection, when the 
bottoms are soft deep mud is tedious but interest- 
ing, and the splashing of an occasional alligator 
removes any sense of monotony. It is surprising 
how many of these areas do not produce mos- 
quitoes although conditions as to food, protection, 
etc., seem to be ideal. After examining many of 
this character the observer is apt to take it for 



68 The Control of Mosquitoes 

granted that Anopheles are absent. There are 
some prolific breeding areas whose importance 
cannot be determined without a thorough and 
painstaking examination. 

Many lagoons, ponds, etc., have been seen 
where larvae were not present near the shore line, 
but were very numerous in protected portions of 
deeper water. Water more than a foot deep, free 
from vegetation, debris, algae, etc., is generally 
non-productive. It often happens that numerous 
larvae are present only in particular parts of a large 
and apparently suitable breeding place, and it 
should be thoroughly investigated before any 
conclusions are drawn regarding its possibilities. 

Again, some areas may produce a species of 
Anopheles larvae only at certain times, and it is 
wrong to conclude that because results are nega- 
tive to-day the conditions will not change sooner 
or later. Seasonal changes have an important 
bearing upon mosquito propagation. 

In clear water such as reservoirs with clean 
edges and abrupt banks, more or less finely divided 
debris collects and is often removed from one side 
of the lake to the other by winds. Larvae are 
frequently present in this mass, and apparently 
the small fish cannot reach them. Marked wave 
action prevents mosquito production. If the 




a 
o 
o 

< 
o 



"■+-3 

ft 

O 



>, 






a 
o 

a 

ft 
o 



3 
o 

ft 

O 



< 



Anopheles Propagation Areas 69 

wind direction is uniform and continuous, larvae 
will be absent on the shore affected by wave action. 
However, if there are small inlets along the shore 
line the wave action may not affect the larvae 
in them, and they will need attention. 

NON-PRODUCTIVE ANOPHELES PROPAGATION AREAS 

In the Cuban anti-malaria campaign as well as 
on the Isthmus, there were so many apparently 
suitable places for mosquito development in 
which the larvae were absent, that attempts were 
made to determine why Anopheles did not oviposit 
in them. The attempts were not successful. 
Larvae were placed in many of these places and be- 
came fully developed. Mosquitoes were some- 
times induced to lay their eggs in non-productive 
places by putting dead grass there. Investigation 
and research along this line is essential. Probably 
new facts will be discovered that may enable us to 
make existing production areas unattractive as 
breeding places and render them sterile. A dark 
brown or reddish substance resembling iron rust 
(name unknown) , which is often accompanied by a 
small amount of natural oil, is found occasionally 
on the Isthmus at the edges of ditches or ponds in 
the form of a limited seepage outcrop and appears 
to be repulsive to Anopheles. Larvae are never 



70 The Control of Mosquitoes 

found in that part of a body of water affected by- 
it, although they are found in other parts of the 
same body of water to which this substance has 
not extended. 

PROPAGATION AREAS CREATED BY MAN 

It is surprising how many mosquitoes are 
unnecessarily brought into existence by people 
who are aware that the construction work they are 
doing will cause Anopheles to multiply. They do 
this even when it would cost no more to arrange 
for proper drainage. Borrow pits or excavations 
are made where they tap seepage water planes, 
and are sometimes left to collect water, in places 
where they cannot be drained. 

River channels are blocked up near settlements, 
flooding hundreds of acres with shallow water. 
Culverts are situated in a way that causes ponds 
to be formed, and streams and ditches to fill with 
silt. They are often entirely closed up, and the 
water allowed to spread where it will. Such condi- 
tions have been created by engineers who knew 
the ensuing results, but were apparently in no way 
interested providing they did not suffer personally 
or financially. 

The additional cost of controlling malaria in 
these localities has been enormous and made the 




Vegetation removed from the edge of a pond at Bohio 



Anopheles Propagation Areas 71 

cost of the anti-malaria campaign very much 
higher than it would have been had sufficient 
authority been given to the sanitary officials to 
prevent the unnecessary formation of hundreds of 
acres of artificially created mosquito-producing 
areas, with the corresponding attendant costs for 
their control, and for the care of sick laborers 
affected. 

DITCHES 

Even where anti-malaria work is being per- 
formed, parts of ditches or pools not kept in proper 
condition will harbor larvae. Any obstruction or 
change of conditions that interferes with the flow of 
water in a ditch, and any condition that brings 
about the breaking of the continuity of the oil film 
may attract mosquitoes. Production is increased if 
the amount of water flowing in the ditch decreases. 

Where the matted algae breaks up and some 
portions of it sink, the direction of the small 
current in the ditch bed changes frequently, and 
increases the number of places and the extent of 
area where larvae may be found. Conditions are 
aggravated if cattle have access to the ditch. If 
treatment is neglected or faulty inspection is 
made, the ditch becomes a menace and produces 
large numbers of mosquitoes daily. The flatter the 



72 The Control of Mosquitoes 

grade the more likely are such conditions to occur. 
The higher the temperature of the water the more 
favorable it becomes for rapid development. 
Anopheles larvae have been taken in ditch water 
having a temperature of 102 degrees Fahrenheit. 

CRAB HOLES AND PLANTS AS SOURCES OF ANOPHELES 

Anopheles larvae have been taken from crab 
holes both in depressions on flat land and on river 
banks which received larvae from receding waters. 
It is known that Anopheles seldom if ever lay eggs 
in crab holes where water is below the ground 
surface. One species of mosquito, which does 
not bite man, habitually lays its eggs in sub- 
surface water in crab holes. It is not an A nopheles. 

While larvae of some species are found in water 
held by stems of plants, and in tree holes, the 
species that enter dwellings and are known to be 
malaria carriers seldom oviposit in such places. 
Propagation in water held by plants and trees was 
not considered of economic importance on the 
Isthmus. 

CHANGE OF SPECIES CAUSED BY CHANGES OF SEASON 
OR OF LOCAL CONDITIONS AT BREEDING PLACES 

It would be natural to expect a prolific source 
of Anopheles albimanus, or Anopheles malefactor , to 




tesult of blocking the Rio Cardenas. A change of species of Anopheles occurred here 



Anopheles Propagation Areas 73 

remain favorable to that species. We do not 
think this to be true. Certain changes take place 
the nature of which is not yet well understood. 
The fact remains that within a short period one 
species will sometimes disappear and be replaced 
soon afterwards by a large number of larvae of 
another species. There are changes in the food- 
stuffs present, formation of algae, plant growth, 
etc., and also other factors and changes that are 
at the present time unknown. Changes of species 
have been observed in relatively large bodies 
of water, such as lagoons, wide parts of rivers 
containing much aquatic growth, and in large 
ponds. In 1913 when the lake at Gatun was 
formed, conditions appeared to be quite favorable 
to the development of Anopheles malefactor and it 
became the prevailing species at Gamboa from 
November, 1 9 1 3 , to February, 1 9 1 4, while previously 
the Anopheles albimanus was more common in 
houses. Since the last mentioned date the Anoph- 
eles albimanus has replaced it and later constituted 
about ninety per cent, of all Anopheles at Gamboa. 
A similar change is taking place at Carlo Camp, 
southwest of Gatun, on the shore of the lake. At 
that point the jungle is flooded with water and 
most of the trees and brush are now dead. Much 
of this growth was alive when the camp was first 



74 The Control of Mosquitoes 

established, about December i, 1913. The month- 
ly Anopheles catch at this camp was, December, 
1 913, 320; January, 1914, 1969; February, 19 14, 
2834. Recently the Anopheles albimanus is be- 
coming the predominating species. 

Strange to say until January, 19 14, there has 
been no influx of Anopheles from the lake at Gatun 
and practically no breeding along the shore of the 
lake near that town, although within a mile 
conditions along the lake shore appear quite 
similar to those near Carlo and Gamboa. Condi- 
tions may change and become favorable at a 
later date. 

OCCURRENCE OF ANOPHELES IN BRACKISH WATERS 

At Cristobal, Beach Island, in the Rio Grande 
valley, and at Gatun, Anopheles larvae have been 
found in brackish and salt water. In the first 
three locations the propagation areas were affected 
directly by tide water. At Cristobal, in that 
part of the tidal flats covered by high tides and by 
excessive tides, larvae were found to be numerous 
wherever clearings were made and leaves remained 
in the water. Clumps of plant stems afforded 
hiding-places to the larvae of Anopheles albimanus 
and Anopheles tarsimaculata, even when small 
fish were present. Invariably larvae were most 



Anopheles Propagation Areas 75 

numerous where the fallen leaves were most 
plentiful. These leaves were about eighteen 
inches wide and four feet or more in length. At 
Beach Island, the wet area, a mangrove swamp, 
was less brackish and well shaded by trees. It 
had a depth of from two to twelve inches and was 
rilled with stumps of young trees relatively close 
together. No algae and very little debris were 
present. The young larvae were more numerous 
than those further developed. The older larvae 
kept closer to the stumps. Probably the fish 
preferred them ; this would account for the relative 
absence of large larvae. In the swampy area in the 
Rio Grande valley the percentage of salt water 
varied with the tide and rainfall. Anopheles 
albimanus was the prevailing species. The deep 
water contained many mangrove trees and drift 
from upstream, while the more shallow water 
was well covered with grass, dead leaves, and 
plants that thrive in brackish water in the tropics. 
Larvae could always be found in untreated portions 
of this area where there were sufficient hiding- 
places. The area was about a mile in length. 

GATUN PROPAGATION AREA IN I913 

The largest influx of Anopheles that occurred in 
the Canal Zone during the canal construction 



76 The Control of Mosquitoes 

period came from a flat depression north of Gatun 
Dam. In making the channel near the entrance 
to the lower lock the material was excavated by 
dredges and passed through pipes onto the area 
referred to. x The canal channel at points where 
the dredges operated was several hundred feet 
wide and subject to the usual rise and fall of 
the tide. Previous to the introduction of salt 
water into this area it produced some Culex but 
not many Anopheles. It was covered with high 
grass and in many places with brush. The 
brush and trees began to die soon after the intro- 
duction of salt water. As the work of filling 
progressed, the increasing body of water spread 
over many acres and this sheet of water, about six 
inches deep, was hidden by tall grass. The water 
was deeper farther off shore. The area was more 
than a mile long and about half a mile wide. 
Flight observations indicated and fairly proved the 
direction the influx was taking before it was known 
by actual inspection of the swamp that this water 
was the source of thousands of mosquitoes that 
affected the settlement from half a mile to a mile 
distant. The water in the grass around the edges 
of the newly formed lagoon remained nearly fresh 
and no salt could be tasted along shore. In some 
1 See Map of Gatun No. 36 



Anopheles Propagation Areas 77 

places where tall grass grew salt was not percepti- 
ble to taste six hundred feet from the shore line. 
In wading out from the shore the water was tasted 
every few yards, and it was noted that young 
Culex and Anopheles larvae appeared with the first 
indication of brackishness. In going farther from 
the shore as the water became more brackish the 
Anopheles larvae found were more numerous and 
more mature. When the water became salty 
enough to be decidedly disagreeable to taste, 
Anopheles larvae were most numerous. They 
were more numerous per unit of area than had 
been noted anywhere on the Isthmus during the 
previous nine years of anti-mosquito work. The 
absence of Anopheles and the scarcity of Culex 
larvae in the wet zone not affected by salt water was 
unique. Tests made along shore at many points 
established the fact. The condition was so 
uniform that by wading slowly from shore to shore 
with eyes closed, and testing by taste alone, we 
were able to reach the infested zone and secure 
larvae in collecting cups. The water surface 
contained large quantities of leaves that had 
fallen from the dying trees. Small larvae-destroy- 
ing fish were quite numerous, but larvae of Anoph- 
eles and Culex were so plentiful in the salty 
water that it was impossible for the fish to make 



78 The Control of Mosquitoes 

any reduction. As time went on the density of 
larvae increased. The observers studying the situ- 
ation were bitten continuously by Anopheles of 
both species while standing in the water in full 
sunlight. The adult species present was chiefly 
Anopheles tarsimaculata although Anopheles albi- 
manus and Culex were very plentiful. This 
was the only time or place on the Isthmus in which 
Anopheles were known to come out into the open 
and bite freely in full sunlight. 

This production area continued in existence for 
several months and frequent analyses of the water 
for sea water content were made. In places where 
the larvae were very numerous the water contained 
sixty per cent, or more of sea water and at times 
above eighty per cent. 

Although the Anopheles tarsimaculata appears 
to thrive best in salty water, yet the larvae have 
been found in fresh water in small quantities, 
and a few adults have occurred ten miles away 
from water affected by tide water. 

METHODS OF DETERMINING THE PRESENCE OR 
ABSENCE OF ANOPHELES LARVAE 

In general we may expect to find larvae in 
relative^ quiet water where aquatic growth, 
vegetation, dead leaves, debris, and twigs have 




Detail of Anopheles breeding ground where flight observations were made 




Grass and plants almost covering the water surface and protecting mosquito larvae 



Anopheles Propagation Areas 79 

accumulated. If not disturbed or frightened 
they can be seen at rest on the water surface but 
often they dive or hide before the observer is 
sufficiently near to notice them. It is not usual 
to find them where such natural protection or 
source of food are absent. Grass and plants 
growing in the water are favorable, but dead 
vegetation appears to be more satisfactory. After 
a little practice an observer becomes expert in 
judging whether parts of a body of water contain 
larvae. It is found convenient to use a small white 
enamel- ware saucer to dip for larvae; this can be 
carried in a coat pocket when not needed. For 
continuous inspection work a white enamel-ware 
dipper is used to advantage. Where vegetation is 
present and larvae are hiding in it, the saucer or 
dipper may be pushed up to the plant or grass 
stalks rapidly, and the larvae drawn out of their 
hiding-places by suction as the water enters the 
saucer, or dipper. This method will obtain larvae 
that are not detected in the water by the eye alone. 
When either of these methods fail, the larvae may 
be detected by the application of larvacide. This 
substance spreads quickly under the water surface, 
and the larvae rise rapidly in their efforts to escape.. 
It is much used in the Canal Zone and many places 
can be rapidly examined by using a small quantity. 



80 The Control of Mosquitoes 

The commercial kresol preparations on the market 
have similar qualities but are more expensive than 
the product we use. If these aids are not at hand, 
fairly good results may be obtained in water 
of less than a foot deep by thoroughly stirring 
up the mud below the water. This generally 
makes the larvae come to the surface in a short 
time. In shallow water where a large number of 
places must be examined in a short time, inspection 
is made by walking in the water and stirring with 
the foot. If grass or debris is present it must be 
pushed or held back to leave a clear area for 
observation. Where the water has almost dis- 
appeared from depressions, or only soft mud 
remains, samples may be washed in clear water to 
determine the presence of larvae. The observer 
should walk along the beds of streams, or the edges 
of ditches or ponds, and examine all places that 
appear favorable, including floating debris on the 
surface of deep water. In ponds and lagoons in 
which tall grass grows examination should be made 
by boat, or if none is available the inspector must 
wade out until he knows the condition of all places 
that may harbor larvae. It must always be re- 
membered that the productive portions of a rela- 
tively large area may be limited to certain small 
ones, either in fresh or brackish water marshes. 



Anopheles Propagation Areas 81 

Seasonal changes must be also borne in mind. 
The unexpected happens very frequently in this 
class of work. 

Only a few of the negro laborers wore hip boots 
for work in deep water. In the wet season the 
sanitary inspectors dressed in khaki, heavy leather 
shoes, and stiff pig-skin leggins. When heavy 
showers fell unexpectedly it was impossible to 
keep dry, and when bodies of water had to be 
examined they waded into them, and let the hot 
sun dry their clothing as it could. It was fortunate 
that the inspectors' enthusiasm lasted longer than 
their clothing ! They found being drenched to the 
skin several times a day less fatiguing than wear- 
ing surveyor's boots for work in lagoons having 
soft mud bottoms. Boots would have been too 
heavy for the amount of walking and work of a day 
in such a hot and humid climate. The leggins were 
essential for protection from thorns, spines, and the 
red bugs that make life a misery to some. 

It is often stated that sewage and polluted 
waters are favorable to the development of 
Culex, and that Anopheles are not found in it. 
This assertion did not hold true under the condi- 
tions in Cuba and Panama. The farther from 
the sewer outlet, the less will be the amount of 
organic substance carried by the water, and a 



82 The Control of Mosquitoes 

point is reached where the quality of the water 
becomes satisfactory to Anopheles. 

In cases where sewers have broken on grass- 
covered hillsides mosquito larvae have been found 
numerous within one to two hundred feet of the 
point of discharge. 



CHAPTER VI 

HARBORING PLACES AND FOOD OF ANOPHELES 

IN uninhabited regions this species feeds on 
* the blood of birds and animals, juices of 
fruits and of plants, and probably on the pollen 
of certain plants. Some observers think that 
blood is the normal food of female Anopheles 
and that other food is taken only when blood 
cannot be obtained. Anopheles apparently try 
to obtain more of it than other mosquitoes. We 
have observed that they do not bite in full sunlight. 
Constant observations on the Isthmus for a period 
of eight years, 1904 to 1912, failed to establish a 
single case. During these years, when numerous, 
they bit freely in the shade of woods. In 19 12, at 
the breeding area of Gatun, direct sunlight on 
brightest days did not prevent six or eight Anoph- 
eles biting the face at one time. The species were 
Anopheles tarsimaculata and Anopheles albimanus. 
They attacked us while up to the knees in water 
as well as on shore. It is interesting to note that 

83 



84 The Control of Mosquitoes 

both species were to some extent afraid of the 
light of a lantern at night in that particular lo- 
cation. If the lantern were behind the neck the 
face was bitten, and on bringing the light around 
toward the face, they immediately ceased oper- 
ations on it and collected on the back of the neck, 
and continued biting vigorously. The same was 
true of the biting of the hands. The hand farthest 
from the light was the one bitten. They invari- 
ably left the lighted side of the hand, if it were 
slowly moved to about eighteen inches from the 
lantern. The same rule held true with regard 
to their settling on the observers* clothing, which 
continually-occurred. This apparent fear of arti- 
ficial lights had been noted in previous years at 
Corozal, three miles from the Pacific Ocean, but in 
that locality Anopheles tarsimaculata were then 
absent and Anopheles albimanus was the prevail- 
ing species. 

When bright acetylene lights with reflectors 
(automobile lamps) were used at Corozal, an 
observer standing in the direct rays and holding 
his bare arms in them ten feet away from the lamp 
was never bitten. Yet when an obstruction was 
placed in the column of light and one inch of finger 
put behind the obstruction, in its shadow, several 
Anopheles albimanus settled on that finger in less 



Habits and Food 85 

than one minute. Four observers were present 
when these tests were carried out. One of the 
men was known to be more attractive to mos- 
quitoes than the others, but when, having started 
with his arms literally covered with Anopheles, he 
reached the zone of a certain intensity of light not 
one remained. They fled with a rapidity similar 
to the movement of people or animals whose eyes 
had been suddenly hurt. In all cases the light 
was sufficiently distant to cause no increase in 
temperature. It is difficult to account for the 
instance of biting in full sunlight at Gatun (near 
the breeding place only) as compared with all other 
cases of absolute repulsion caused by artificial light. 
Of course it is possible that the Anopheles at 
Gatun bit us while in the sunlight because other- 
wise they could never have obtained any blood. 
Their natural instincts are difficult to determine. 
In general, they are most ravenous at dusk and 
soon after daylight. When numerous they bite 
freely in shady places near the production area 
and at places distant from it where they rest during 
the daytime. Many were noted less than a foot 
above the ground on the leeward side of trees near 
the breeding area. On one tree forty- three were 
counted. 

In a similar manner they are found on wire 



86 The Control of Mosquitoes 

screens on the leeward side of houses in large num- 
bers while absent from screens on the windward 
side. At Gatun, when the mosquito influx was at 
its maximum, they were found at rest in brush and 
under dead grass on the wind-swept hillside, in 
large numbers under houses, and in any place that 
afforded protection from sun and wind. This 
condition existed for several months during the 
dry season. No natural flight in the sunlight has 
yet been observed. While, no suitable hiding 
places except vacant houses were without mos- 
quitoes in the daytime, yet beyond the settled 
area none were found. They only rested in places 
between the brackish body of water and the vil- 
lage limits; and when grass in which they were 
resting was disturbed in the full sunlight they flew 
about ten feet to the next nearest shaded place. 
Large numbers were collected under houses 
where the breeze was sufficiently strong to make 
the lighting of a match difficult. These inhabited 
houses were on posts from two to ten feet above 
ground. The dry weather ground-cracks under 
the houses were several inches deep and the mos- 
quitoes collected in them, but when small bunches 
of grass or dry hay were placed under the houses 
they hid in these in preference to the cracks. 
None rested on the floor beams under the houses, 



Influence of Prevailing Wind Direction 
and its relation to Anopheles entering houses. 




AvAt-time of 'wind Anopheles collect at rear of house, 
(leeward side). 
Door ( b) is the danger point. 
Door (a) may be held open by wind. 
Arrows denote resting or .collecting places of Anopheles. 




t t i tt t t 
B;- Screened porch advantageously located* 



Diagrams showing best locations for screen doors 



87 



Influence of Prevailing Wind Direction 
and Its relation to Anopheles entering houses. 




\t t t 



C- Anopheles collect on screen 
and enter if door is left 
open long enough. 



t ft 

A Door in a re-entrant 
angle facilitates entrance 
of mosquitoes. 
They enter when the door 
is opened. 





Thedoor of screened porch (E.) is better located than that at (F). 
ff ft Anopheles 

Diagrams showing best locations for screen doors 



88 



Habits and Food 89 

where there was enough light to read by with 
comfort. 

In order to determine to what extent the mos- 
quitoes rested in the shade under houses, mos- 
quito bars were hung up to clear the ground by a 
few inches. A laborer was placed under each net. 
The mosquitoes did not hesitate to leave their day- 
time resting places and soon reached the nets, 
where they were collected. Account was kept 
of the number taken between six-thirty a.m. and 
five p.m. During a period of twenty-two days it 
was observed that thirty- three per cent, of their 
total number entered the nets between six-thirty 
and eight A.M. The total catch by this method 
under five houses in the same period was 14,322 
adult Anopheles, mostly Anopheles tarsimaculata. 
These came from ground-cracks under the house 
and from the small quantity of dead grass that had 
blown there. In another five-day test, with a 
man under a mosquito bar beneath each of the 
five houses, 4389 female and 132 male Anopheles 
tarsimaculata were captured inside the nets. All 
these mosquitoes had been resting on the ground or 
in the ground-cracks under the houses. By poking 
the cracks with a stick they were disturbed, but 
flew away only a few feet to another hiding-place; 
none went out into the open where the sun was 



90 The Control of Mosquitoes 

shining. Although so many were under the houses 
none came out to bite anyone standing in the sun. 

The Gatun salt-water swamp was the source of 
these mosquitoes. 1 The houses affected were 
numbers 3, 184, 185, 195, and 220, located near the 
railroad depot. 2 There are many other houses 
at Gatun, some less and some equally distant from 
the propagation area. Under most of them no 
mosquitoes were present in the daytime. 

Although it is customary for mosquitoes to bite 
soon after sunset, cases have been known where 
observers remaining in one place from six p.m. were 
not bitten until eleven p.m., when Anopheles 
albimanus became suddenly numerous and fed 
freely. When the jungle surrounding houses was 
cleared, for several days mosquitoes entered them 
in much larger numbers than before the clearing 
was made. It is said that a fairly brisk wind 
prevents the flight and biting of mosquitoes, but 
on the Atlantic slope where the trade winds blow 
nearly all the year round, they often bite at dusk 
whether the wind blows or not. In infested settle- 
ments mosquitoes are seldom found in vacant 
houses. 

When houses are imperfectly screened Anopheles 
are more apt to find defects than other mos- 

1 See map p. 101. a See map p. 101. 




Oh 

cu 

w 

I 



CD 

d 
o 

a 

o 






2 

o 

CD 



CD 

"d 
a 
3 



*d 
o 



CD 



CD 



^ 



Habits and Food 91 

quitoes, but they have difficulty in finding their 
way out of buildings. In the daytime, they are 
more commonly found in the bedrooms than in any 
other part of the house. 

Some people are more attractive to Anopheles 
than others. One of the sanitary inspectors was 
known to possess this quality, and the arms of 
three men were placed around his bare arm, so 
that any Anopheles desiring to bite him had to 
find their way to him through an inch wide opening 
between the bared arms of two other men. Several 
Anopheles albimanus did this. Some time later 
the same person and two observers trying to locate 
the principal source of Anopheles causing the 
influx at Cristobal were not bitten once from dusk 
to nine o'clock. A brown horse nearby was 
examined and found to be well covered with 
Anopheles albimanus. The observers sat down 
near the animal, but failed to attract a single 
mosquito in thirty minutes. They then began 
to catch the Anopheles that were biting the horse, 
using chloroform tubes: the mosquitoes attacking 
the horse arrived more quickly than they could be 
captured and kept the party busy. The catch- 
ing was continued for an hour, and during that 
period none of the men were bitten. They had 
lamps and noticed that no mosquitoes settled on 



92 The Control of Mosquitoes 

their clothing, although they frequently examined 
the parts which were not exposed to the direct 
rays of light. 

Mosquitoes not only enter trains to bite people, 
but remain in passenger cars that are in motion 
for long periods during the night time ; they usually 
leave the car soon after daylight. Some are 
accidentally trapped in train closets and freight 
cars and are then transported long distances. 

The importance of Anopheles settling on people's 
clothing, and being transported long distances and 
into screened houses has not received the attention 
it deserves. Cases have frequently been noted 
in which they remained on a man's coat during a 
stiff wind while he walked a hundred yards; and 
even longer transportation by this means, or on the 
backs of animals, is quite possible. 

While flight observations were being made at 
Gatun, a chicken coop was examined at eight 
o'clock on two consecutive nights. The observers 
were bitten by Anopheles while watching the 
chickens, but failed to note any mosquitoes trying 
to bite the fowls. The Culex resting in large 
numbers on the chicken roost were not gorged and 
did not bite the fowls, but their position gave 
them shelter from the breeze. Those outside this 
shelter bit us freely. 



Habits and Food 93 

In one instance three mosquito bars were placed 
in the woods for one night with a man under one 
bar, a dog under the second, and a coop containing 
fowls under the third. The net with the man 
collected 274 Anopheles and fifteen Culex, the 
dog's net had five Anopheles and nine Culex, and 
the fowls' net contained twelve Anopheles and six 
\yUvex » 



CHAPTER VII 

FLIGHT AND ATTRACTION OF MOSQUITOES 

THE various species of mosquitoes have not 
the same habits. The differences of time 
of biting, of selection of propagation areas, quality 
of water in which larvae are found, etc., are well 
known. Every night at certain periods of the year, 
hundreds of Culices are found dead in the globes of 
electric arc lights. Anopheles on the contrary are 
practically never found in the globes and will not 
fly close to a bright light. Apparently only a few 
species of one genus of mosquito are attracted by 
light sufficiently to be destroyed by the flame, 
while the Isthmian Anopheles and possibly others 
find a strong light repulsive. It is possible that 
some Anopheles associate lights with man. 

The general direction of the wind at Panama is 
from north to south and it blows from south to 
north on but few days in the year. Many years of 
careful observation on the Pacific slope of the 
Isthmus gave fairly conclusive evidence of a marked 

94 




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Flight and Attraction of Mosquitoes 95 

flight of Anopheles in a northerly direction, or 
against the wind, and this was reported by Le 
Prince at the International Congress of Hygiene, 
1912. 

Anopheles propagation areas occur near Ancon 
and the city of Panama, and the wind blows from 
those places toward the houses: if the flight of 
Anopheles was assisted by gentle winds the houses 
should contain many. 1 As a matter of fact, 
there are few at Ancon as compared with other 
settlements, and the production area there has been 
under observation for nine years. 

Panama touches the Pacific Ocean. Beginning 
at the base of the hill on which Ancon, its suburb, 
is located, a swampy area extends for about two 
miles northwards, and the village of Corozal is 
three miles north of Panama. Three miles north 
of Corozal is the village of Miraflores, and a 
prolific Anopheles-breeding area lies between the 
two villages, extending over the larger part of 
the intervening distance. The southern end of this 
area is nearer Corozal than any part of the Ancon- 
Corozal swamp. 

In 191 1, work was concentrated on the southern 
portion of the Corozal- Miraflores swamp, in order 
to reduce the Anopheles arriving at Corozal. The 

x See map opposite p. 95. 



96 The Control of Mosquitoes 

work on the windward side was ineffective, and the 
influx of Anopheles albimanus increased. Work in 
this swamp was then stopped and the force con- 
centrated in a larvae-infested portion of the Ancon- 
Corozal swamp about a mile south of Corozal. 
Since the latter area has been controlled no large 
influx of Anopheles has taken place at Corozal, 
except during short periods when the wind changed 
and blew from south to north. 

The large swamp between Corozal and Mira- 
flores was difficult to control in a satisfactory 
manner. It was neglected for a certain time to 
ascertain if, when producing Anopheles at its 
maximum capacity, many of them would reach 
Corozal, traveling with the wind. Apparently 
this did not happen, as the number of adults at 
Corozal did not increase while the other area a mile 
to the south of Corozal was kept under proper 
control. 

Soon after the Corozal-Miraflores area was 
purposely neglected the catch at the laborers' 
barracks at Miraflores increased and the influx 
continued. The maximum catch in a single trap 
on one night was more than a thousand. This 
trap was attached to an 8" x 24" opening in the 
screening and the total area of small openings in 
the trap screen through which mosquitoes passed 




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Flight and Attraction of Mosquitoes 97 

was less than eight square inches. During this 
high influx at Miraflores the low catch at Corozal 
continued. The most prolific part of the interven- 
ing production area was much nearer to Corozal 
than it was to Miraflores. 

Is it the usual custom for this Anopheles to fly 
against light breezes ? Is it possible that they are 
attracted by scent? Or when the number of 
Anopheles being produced in a limited area amounts 
to millions, do the habits of flight to obtain blood 
then change? These questions are exceedingly 
difficult to answer, but as they are of the utmost 
importance in successful and economical control 
of Anopheles they should be investigated. 

The increase or decrease of electric lights in 
buildings apparently does not make much difference 
in the number of Anopheles entering. In several 
instances, by increasing the amount of light in a 
small experimental house at Corozal, the number 
of Cidex (species not determined) increased even 
when vacant. When the building was empty or 
without lights, only an occasional Anopheles 
entered, but when one or two men were sleeping 
in the building Anopheles crowded through small 
openings and bit them whether the building was 
lighted or not. 

Where buildings are well screened and Anopheles 



98 The Control of Mosquitoes 

outside are numerous, they will try to force their 
way through incredibly small cracks or defects in 
the screen. Many cases have been noted where 
they have become tightly wedged in their efforts 
to pass through openings that were too small, and 
then were unable to free themselves. While this 
experimental work was being done it was found 
that although the breeding of Anopheles pseudo- 
punctipennis and Anopheles malefactor was taking 
place much nearer to the buildings at Corozal than 
Anopheles albimanus, mosquitoes of the former 
species were not found at Corozal camp. It is 
evident, from the long-distance flights described 
above, that in some instances it was essential to 
locate and control the principal source or sources 
of Anopheles , which although more distant than 
other propagation areas located relatively near, 
may be, and in the two instances above mentioned 
actually were, the source of malaria-carrying 
Anopheles that reached the houses. 

Gatun, about seven miles south of Colon, is one 
of the largest settlements in the Canal Zone. 
Above five thousand canal employees live there. 
Between January and March, 191 3, more mos- 
quitoes were found there than had been found in 
any settlement since work began on the canal. 
The weekly catch of the Anopheles that gained 




Experiment Station, Corozal, where studies 
were made of mosquito attraction by light 



Flight and Attraction of Mosquitoes 99 

access to the interior of dwellings varied from 7000 
to 22,000. It was necessary for office men to burn 
smudges and wear leggins. The seats of cane- 
seated chairs were covered with paper, and many- 
devices invented to make life more pleasant. 
During the worst part of the period of influx any- 
one out of doors at dusk was bitten many times 
per minute. 

It was evident that some new source of Anopheles 
had been brought into existence. Wherever anti- 
malaria work had been done before, all known 
production areas were thoroughly examined, but 
gave no clue to the new situation, as they were 
in normal condition. The area under inspection 
for propagation places was extended. Mosquitoes 
were present in the daytime in all places sheltered 
from the sun and wind, except at the east of the 
settlement. To the south, was the shore of Gatun 
Lake along which much plant growth, debris, and 
floating islands collected. Certain aquatic plants 
were growing in solid masses from the shore line out 
into the water, and filled the spaces between the 
floating islands that had collected near the shore. 
Vines were growing on the debris, and the floating 
mass was more or less continuous along the shore. 
All of this new possible production area was care- 
fully examined and very few larvae were found. 



ioo The Control of Mosquitoes 

The daily inspection was supplemented by night 
observations; the shore and the lake just off shore 
being observed. No mosquitoes were present on 
the lake at night and people in small boats close 
to the lake shore not far from the settlement were 
not bitten. It was evident after making many 
observations that the lake was not the source. 
Careful examination of all the territory to the 
north of the settlement failed to show any breeding 
places of sufficient extent or importance to account 
for the influx. The area to the west was examined 
last, because of the extensive cleared area west of 
the settlement which was known to be free from 
possible breeding places. r 

To the west of the old French canal there was 
some flat land into which the sea water and mud 
from the American canal was being pumped. This 
place had never before produced mosquitoes that 
affected Gatun, and was so located that to reach 
the settlement the adults would have to fly from 
half a mile to a mile straight across or at right 
angles to the stiff breezes which prevail at Gatun in 
the dry season, over ground containing very little 
protection from wind by high grass or bushes. 
Flight of this length under such conditions was 
not thought to be possible. Between the wet area 

x See map. 




C 

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Indicates houses where stained 
Anopheles were retaken 




Map of Gatun: Showing Anopheles propagation area and houses where stained specimens were recaptured 



Flight and Attraction of Mosquitoes 101 

formed by dredging operations and the French 
canal, and parallel to the latter, was a strip of 
woodland and heavy brush having a width of from 
one to two hundred yards. In this thicket mos- 
quitoes were more numerous than at any other 
place in the Gatun district or on any area examined 
in trying to locate the source of the influx. The 
larvae in the water and the mosquitoes near were 
numerous enough to account for the influx at 
Gatun; but was this the source? That was the 
important question to determine. 

Several volunteer investigators visited the 
thicket at night and retreated in a very short time. 
After slowly rowing up and down the French canal 
at night it was determined that very few Anopheles 
were crossing that body of water. The party 
was seldom bitten until the boat was fastened to 
the bank, when it was bitten unmercifully. The 
same results were noted on successive nights and 
doubts arose as to whether this newly created 
area had any connection with the Anopheles at 
the houses about a mile distant. The surrounding 
country was again examined but with negative 
results. It was assumed that the enormous 
number of mosquitoes produced every twenty-four 
hours at the brackish water production area must 
of necessity spread out or travel a long distance to 



102 The Control of Mosquitoes 

find blood sufficient to satisfy them. It appeared 
within the limits of possibility that they might fly 
high at night during the lulls in the wind, and not 
be noted by people in boats on the French canal. 
The assumption was also made that the period of 
long flight might be of limited duration. Other 
factors bearing on the problem and all previous 
information obtained relating to Isthmian mos- 
quitoes were given due consideration. We contin- 
ued the investigation, beginning by making several 
careful observations on the French canal lasting 
more than twenty-four hours each before reaching 
any partial conclusions. 

On January 20, 191 3, at 4.30 p.m., two ob- 
servers were posted on the opposite bank of the 
French canal from the propagation area, and, facing 
the latter, watched carefully for any indication of 
flights. They were prepared for a twenty-four 
hour watch, although extra night work had robbed 
them of much sleep in the past week. For two 
hours nothing happened. At 6.20 p.m. birds ap- 
peared in the air, apparently catching insects. 
They were at an elevation of thirty feet or more 
above the water surface. A little later it was 
noted that these birds fed at a lower elevation. 
At 6.30 interest deepened. The birds kept on 
feeding and then flew rapidly back and forth at six 




Floating islands blown toward Gatun 




Masses of aquatic plants and floating islands in Gatun Lake 



Flight and Attraction of Mosquitoes 103 

feet or less from the water surface. It was then 
that Le Prince, looking over the side of a flat 
bottomed boat toward the clear sky line, dis- 
covered the first appearance of the flight of Anoph- 
eles accompanied by Culex. The flight was from 
west to east and quite marked. He then selected 
a place on the opposite bank of the canal from the 
propagation area and faced it. As it became 
darker, the quantity of flying Anopheles increased, 
and, by bending low and looking past a dark 
object at the clear sky line, hundreds of Anopheles 
could be seen passing by in one definite direction. 
They not only traveled in a fixed direction but 
many appeared to hurry about it. After dark the 
flight was reduced to practically nothing. During 
the period of flight, the observers were bitten 
continuously. Soon after the flight ceased one 
could remain on the east bank (in the path of the 
recent flight) and be attacked only once or twice 
in an hour's time. All night long on the west 
bank, near the propagation area, and between it 
and the French canal, hundreds of mosquitoes 
surrounded and bit an observer. There was no 
secondary flight period, although observers re- 
mained to note if this occurred. 

During subsequent evenings, the flight was 
recorded; it started about the same time each day. 



104 The Control of Mosquitoes 

On the second evening, directly after the birds 
arrived and began feeding, several were shot and 
examined. It was found that they were catching 
the Anopheles, some of which were found in their 
throats. These birds are called ' ' night- jars ' ' ; they 
were feeding between thirty and forty feet above 
the canal and had not fed at a lower elevation. 

After the flight direction near the canal was 
ascertained points of observation were selected 
between it and the settlement, and the direction of 
flight was noted to be relatively constant. When 
the winds came in short strong puffs, the Anopheles 
headed directly into it, but "skidded" sideways 
and were able to fly for short intervals at right 
angles to the direction they were facing. Some 
remained on the wing in a fixed location and as 
soon as they succeeded in controlling themselves, 
and conditions were right, dashed off eastward, at 
right angles to the direction of the wind. This 
forward flight of Anopheles tarsimaculata and 
Anopheles albimanus was so decidedly marked 
that after its discovery by the senior author it was 
easily noted by many, including those who at 
first scarcely believed it could be true. No one 
in the entire area so thickly infested noticed the 
flight direction until instructed how to observe it. 

It was thought that with thousands of mos- 



Flight and Attraction of Mosquitoes 105 

quitoes traveling from the swamp to the settle- 
ment each night, an appreciable number might fly 
beyond the settlement. 

Large numbers passed occupied houses and 
appeared at more distant ones; but apparently 
none passed the houses most distant from the 
breeding area. We remained in the shade in the 
day and thrashed the bush for a hundred yards 
beyond the settlement and stayed there at night 
without securing any specimens. Yet during 
this period they were present in practically all 
occupied houses, and particularly numerous in 
screened houses where the doors were frequently 
used, as at the hotel, Y. M. C. A. building, bache- 
lors' and laborers' barracks, etc. 1 

The results of the numerous observations showed 
that the Anopheles knew where they desired to go; 
that they traveled in a direct route at practically 
right angles to a strong breeze, and that large 
numbers went forward between 6.30 and 7.00 p.m. 
daily. It was not ascertained whether any of them 
made more than one forward trip to the feeding 
ground. It may be that several trips were taken, 
but had none returned the thousands passing out 
daily were sufficient to continue the influx at the 
settlement. 

1 See map opposite p. 101. 



106 The Control of Mosquitoes 

As it was definitely proved that the forward long- 
distance flight was of limited duration and occurred 
just at dusk, it was assumed that there should be a 
visible return flight at or before dawn. The first 
morning this was carefully waited for from mid- 
night to 6 a.m. but did not occur, and the observers 
noticed very few mosquitoes, although thousands 
had passed them on the forward flight. It was 
thought that there must be a return flight to the 
propagation area of a nature not yet understood. 
It had been noted that at the start of the forward 
flight (i.e. over the canal) the Anopheles were forty 
feet up in the air, and it was possible that the end 
of the return flight was also above the range of 
vision. Additional investigation, however, showed 
that there was a marked return flight and though 
this happened on several successive mornings, other 
mornings showed practically no return flight from 
the village, or houses, to the breeding place, so far 
as could be noticed. This return flight did not 
begin until 6.00 a.m. although there was sufficient 
light to read by ten minutes before that time. 
The return flight, once fairly started, was of much 
shorter duration and more rapid than the forward 
flight. The • ' night- jars" accompanied the return 
flight, but were absent on those mornings when no 
return flight occurred. As the daylight became 







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Flight and Attraction of Mosquitoes 107 

stronger the speed of the returning Anopheles 
increased. The termination of both forward and 
return flight was remarkably abrupt, or as one ob- 
server expressed it, "the flight stops with almost 
mechanical precision when there is too much 
daylight or too much darkness." 

As already mentioned, the Anopheles travel at 
incredible speed toward the end of the return 
flight. The only change taking place was the 
increasing intensity of light. This, together with 
the fact that when sheltering from the wind or sun- 
light they will remain hungry rather than fly 
three feet out into the sunlight to bite a person 
standing in the sun, but will immediately attack 
him if he steps into the shade, is at least sug- 
gestive. Are both heat and a certain intensity 
of light repulsive to Anopheles, or is it the light 
only ? The latter would seem to be the case under 
natural conditions, as they do not come out into 
the sun to bite after 7.00 a.m. One of the obser- 
vers, Mr. Zetek, noted some males in the return 
flight, and also found blood in the mosquitoes 
returning. 

During the flight observations Mr. E. F. Quimby 
conceived the idea of using an apparatus for 
registering the direction of the flight of Anopheles 
with a view to determining the direction of, and 



io8 The Control of Mosquitoes 



^T^> 



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the area covered by, heavy flights. The appara- 
tus is here shown. It consists of four glass plates 
set in a metal frame; the latter mounted on a 

tripod. The 
plates are set in 
two vertical 
planes at right 
angles to each 
other. The in- 
struments can be 
set up so that 
the plates point 
north, south, 
east, and west. 
The glass was 
painted with a 
mixture of resin 
and castor oil 
giving a practi- 
cally transparent 

A device for showing flight direction of coating capable 
Anopheles rf hdding any 

mosquitoes that came into contact with it. The 
solution was made by adding small quantities of 
pulverized resin to heated castor oil; constant 
stirring was necessary. The proportions used 
were one quarter pound of resin to a pint of castor 




Flight and Attraction of Mosquitoes 109 

oil. The instrument was used and the results 
obtained checked with the results of personal ob- 
servations on both forward and return flight, with 
the exception of one case, where a male Anoph- 
eles was apparently traveling at least, temporarily 
in an opposite direction from the main flight. 

It is possible that where anti-malaria work is to 
be taken up in badly infested regions observations 
of flight made in connection with this apparatus 
will indicate which, of several possible production 
areas, is the principal source of the particular 
species of mosquito that it is desirable to eradicate. 

One interesting feature in connection with this 
long-distance flight was that the malaria sick-rate 
did not increase much although the number of 
malaria-carrying species of Anopheles present 
in houses increased enormously. Eight men were 
employed daily catching mosquitoes in houses at 
Gatun. The indoor catch of each week and 
corresponding cases of malaria are given in the 
table on the following page. 

Although, as already stated, long flights of 
mosquitoes on the Isthmus were known to some 
of us, we were unfortunately unable to trace any 
individual mosquito and find out by actual obser- 
vation how far it went, and in what direction. 
The necessity for this information was apparent. 



no The Control of Mosquitoes 

The chief sanitary inspector assigned to Mr. J. 
Zetek the task of marking mosquitoes in such 
a manner that they could be recognized. We had 
previously tried to induce them to mark themselves 



Week ending— 



Number 


Malaria 


of adult 


cases per 


Anopheles 


week per 


destroyed 


1,000 em- 


in houses. 


ployees. 


207 


2.7 


149 


3.5 


109 


4.5 


404 


2.5 


666 


6.8 


779 


6.8 


3,397 


6.1 


3,150 


10.1 


3,296 


6.1 


5,430- 


6.1 


9,415 


3.9 


11,698 


5.0 


22,074 


4.1 


22,988 


5.5 


19,873 


6.2 


15,746 


7.5 


15,580 


8.2v 


15,676 


9.3 


11,441 


6.8 


11,234 


5.4 



Percentage 
of employ- 
ees sick 
with -ma- 
laria. 



Oct. 19 . 
Oct. 26.. 
Nov. 2. 
Not. 9. 
Nov. 16. 
Nov. 23. 
Nov. 30. 
Dec. 7., 
Dec. 14. . 
Dec. 21.. 
Dec. 28a 
Jan. 4.-. 
Jan. 11., 
Jan. 18.. 
Jan. 25.. 
Feb. 1... 
Feb. 8.. 
Feb. 15.. 
Feb. 22.. 
Mar. 1... 



Per cent. 

0.27 
.35 
.45 
.25 
.68 
.68 
.61 

1.01 
.61 
.51 
.39 
.50 
.41 
.55 
.62 
.75 
.82 
.93 
.68 
.54 



Table showing number of Anopheles caught in houses at Gatun 
each week during the heavy influx 

with red ink while escaping from cages, but the 
experiment failed. Fortunately Mr. Zetek solved 
the problem before the influx at Gatun took place. 
The method devised for following up the individual 
mosquito was as follows : 

Larvae and preferably pupae of Anopheles were 
collected and developed into adults. These were 
placed in cages, protected from sun or wind, and 



Flight and Attraction of Mosquitoes in 

stained with an aqueous solution of an aniline dye. 
They were given a period of rest and liberated 
toward evening. Aqueous solutions of eosin, me- 
thylene-blue, etc., were used, one gram of dry stain 
to fifty cubic centimeters of water. An atomizer 
was used to direct a fine spray upon the mosquitoes. 
When spraying care was taken to avoid covering 
them entirely with the stain ; only minute particles 
were allowed to touch them. It was found that too 
much stain rendered the mosquitoes useless 
for purposes of experimental flight. The stained 
mosquitoes were liberated at known distances 
from the laborers' barracks at Corozal and to the 
south of it. All mosquitoes noted in the building 
at that camp were carefully collected; those from 
each house placed in a separate box, dated and 
labeled. Later they were placed on a glass plate 
that rested on white paper and spread out. Each 
one was treated with a small amount of a solution 
that dissolved the dye on any stained specimen. 
When stained specimens were encountered, the 
color was seen to be present as soon as the testing 
solution came in contact with it. The solvent 
for testing consisted of three parts alcohol, three 
parts glycerine, and one part chloroform. As a 
result of this method of staining and consequent 
ability to follow the movement of mosquitoes 



ii2 The Control of Mosquitoes 

near Corozal, the previous northward flight al- 
ready referred to (i.e. against the wind) was 
established beyond a doubt. One of the many dif- 
ficulties in this work at first was due to seasonal 
changes. 

From time to time the supply of mosquitoes 
gave out and we had to transport larvae and pupae 
across the Isthmus ; many died of the rough han- 
dling and shaking unavoidable with inexperienced 
collectors, and when many larvae must be collected 
quickly. 

At Gatun, where staining methods were again 
used to check the flight already observed, we 
collected mosquitoes in tents near the breeding 
places, and also tried small paper houses. The 
work was tedious, and it was difficult to move 
about in such small places, or to keep quiet while 
being bitten by hundreds of mosquitoes and still 
more sand flies. This method of collection was 
replaced by using mosquito bars. They were hung 
up in the woods and the lower edges pinned up and 
kept a few inches from the ground. It was soon 
found that by occasionally brushing the mos- 
quitoes from the hands, face, and clothing, they 
would fly upwards and eventually come to rest 
in the upper part of the net. Sometimes they 
were but half an inch apart. This method was so 




Staining Anopheles with aniline dye to determine 
length of flight 



Flight and Attraction of Mosquitoes 113 

successful that other methods of collecting were 
abandoned. 

When the first net was installed the biting was so 
continuous that after it became well filled with 
mosquitoes the observers crawled out from under 
and tied up the bottom of the net. Conditions 
were becoming unbearable even to those persons 
who were accustomed to be bitten frequently. 
Next morning soon after daylight nearly all the 
mosquitoes within the bar were dead, apparently 
killed by the drying action of the wind during the 
night. After this experience, as soon as a sufficient 
quantity of mosquitoes collected in the upper parts 
of the mosquito bars, they were sprayed very 
lightly with aqueous solution of aniline dye and 
liberated by turning the mosquito bar inside out. 
This operation was repeated as long as the obser- 
vers could keep their tempers, and then a general 
retreat was made to the other side of the canal 
where there were no mosquitoes. 

Very patient negroes were necessary to act as 
bait under the mosquito bars! Had the boat 
used for crossing the canal been conveniently near 
the bait might have escaped. Many of the stained 
mosquitoes were recovered, and even two weeks 
after the last catch was stained, some of them were 
captured near the place where the nets had been. 



ii4 The Control of Mosquitoes 

Considering the small number that were stained 
compared with the enormous number that took 
part in the Gatun flights, it was not to be expected 
that many stained specimens would be recaptured. 
Forty stained specimens were recovered at dis- 
tances varying from 1200 to 6250 feet from the 
liberation station: 

2 between 1000 and 2000 feet distant 



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" 3000 " 





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3000 


" 4000 " 


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4000 


" 5000 " " 


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" 6000 " 


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6250 " 



At the time of the staining the Anopheles 
tarsimaculata was the most numerous species, 
although Anopheles albimanus and Culex were 
present both at the breeding place and in the 
flight. Among the specimens recovered, thirty- 
three were Anopheles tarsimaculata; five Anopheles 
albimanus; one Culex, and one undetermined. 
Some of them were captured in mosquito bars 
under houses. Of the five that made the longest 
flight, four were Anopheles tarsimaculata and 
one Anopheles albimanus. They were caught by 
an observer under a net placed in the shade of a 
building 6250 feet from the liberation station. 



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Anopheles in a mosquito-bar exposed to air currents at night 



CHAPTER VIII 

ATTACK ON PROPAGATION AREAS BY FILLING 

IN beginning anti-malarial work near a village 
* where this work has not been done before, 
the filling of depressions, etc., that hold water 
should be accomplished. These places may be 
controlled by the application of oil or larvacides, 
but this method is not as good, because the work 
needs to be repeated at frequent intervals, and also 
because the personal equation is involved and 
some propagation areas may be left untreated suf- 
ficiently long to produce one or more broods. All 
small depressions that hold water, including cow- 
hoof marks, badly cut-up land, wheel-track marks, 
small ponds that cannot be drained satisfactorily, 
and flat lands that do not dry with sufficient 
frequency to prevent the development of pupae 
during the wettest periods, should receive atten- 
tion. There is nothing to be gained by filling 
depressions having such absorbent qualities that 
they become dry before a brood of mosquito 

115 



n6 The Control of Mosquitoes 

larvae can mature. Lowlands that cannot be 
drained and those parts of extensive swampy 
land that produce Anopheles can often be filled 
to advantage. 

It is also important to enact laws preventing 
excavation or filling from becoming the source of 
new broods of mosquitoes. In borrowing material 
for fills, relatively porous material should be se- 
lected, if available, because depressions in a fill 
made of clay will retain rain-water. If the ma- 
terial is taken from a hillside, the bottom of the 
borrow pit should be left properly graded. 

If seepage planes are suspected, the proposed 
site of the borrow pit should be examined with 
an earth augur to determine the depth of any 
seepage plane that may be present, and the 
borrow-pit floor must be kept well above the damp 
soil overlying the plane of seepage. If this is not 
done it may become necessary, later, to install 
seepage intercepting ditches to take care of the 
borrow pit. The finished surface of fills should be 
properly graded and allowance made for subse- 
quent settlement, which always takes place after 
filling. 

Attempts to cover wet places where subsurface 
water under pressure is the difficulty will often 
fail when a fill is shallow, and the entire new fill 



Attack by Filling 117 

may become saturated. If there are but a few 
springs or sources of water, the fill can be kept 
dry by making small ditches care for the water. 
It is more economical and satisfactory to treat 
flat ditches than to attempt to oil wet grass- 
covered areas. In the latter case, as the work is 
performed by laborers who are fatigued by carry- 
ing loads of oil in mud and water all day long, we 
cannot count on their vigilance to ensure the entire 
surface of every small body of water covered by 
grass being completely covered by oil. Consequent- 
ly it is essential to use large quantities of oil and 
thoroughly saturate all of the wet land. The area 
of the ditch as compared with the area of the wet 
land to be filled will indicate the relative cost 
of oiling each. Small areas are filled by pick, 
shovel, and wheelbarrows. For larger areas 
where suitable material is near, drag scrapers 
or wheel scrapers drawn by horses are used. 

On the Isthmus much excavated material was 
available and many acres were filled by dump 
cars and Lidgerwood cars from which the mate- 
rial was removed by a plow drawn by a steel 
rope. On some of the heavy or deep fills made 
by dump cars the soft land at the toe of the new 
fills was sometimes thrust up by the weight of the 
fill or rolled up in front of it. In making fills of 



n8 The Control of Mosquitoes 

this nature when the heavy rocks roll down the 
slope faster and go farther than the accompany- 
ing earth, it generally happens that a layer of 
rocks and boulders lies under the heavy fills thus 
made. 

Much of the rock used in filling taken from Cule- 
bra Cut decomposes rapidly when exposed to the 
air, and turns into soil in a few months time. The 
freshly made dumps are at first sufficiently porous 
to absorb the rain-water that collects in the low 
parts of the uneven surface of the dump. However, 
in a year's time settlement takes place and also the 
impervious particles of the decomposed rock as 
well as clay are washed by storm water into the 
depressions. When the depressions cannot be 
economically drained it is frequently possible to 
get rid of the water by leading it down to the 
spaces in the layer of loose stones at the bottom 
of the dump. This is done by drilling a hole 
near the pond and using a little dynamite. 

Within a year's time the new dumps on the 
Isthmus were covered with dense vegetation and 
had to be frequently inspected as the older they 
became the more numerous were the small surface 
pools. 

The vegetation may make travel difficult. 
Sometimes it is burned in the dry season, to facili- 



Attack by Filling 119 

tate the finding of newly formed breeding places 
at the early part of the wet season when much 
Anopheles production takes place. 

After the deep fills are made there is sometimes 
a considerable flow of water under them, which 
outcrops near the toe of the fill and has to be cared 
for, either by an intercepting ditch, or by oiling. 

HYDRAULIC FILLS 

In digging the canal channel near the Pacific 
and Atlantic terminals, pipe line dredges were 
used. These dredges cut the material near the 
suction end of the pumps and draw it in with 
the water. This muddy liquid, containing from 
ten to twenty per cent, of solid material, is then 
forced through pipe lines for long distances. The 
lowlands are surrounded by dykes and the liquid 
mass fills the enclosure. When the surface water 
is at first drained off, the mass of silt and mud 
dries very slowly. Its depth may be anywhere 
from one to ten feet or more. 

In many places pools and depressions produce 
mosquitoes before the fill has time to settle and 
dry. As the mud dries numerous cracks are 
formed which catch and hold rain-water. As the 
drying proceeds the cracks widen from a fraction of 
an inch to three inches and sometimes are more 



120 The Control of Mosquitoes 

than a foot deep. The dried surface soil is at first 
merely resting on liquid mud and if a person stands 
on one of the solid portions it frequently sinks 
beneath him. When the crust becomes thicker, the 
cracks are more numerous, and so are the numbers 
of Anopheles developing in the cracks after showers. 
To control similar conditions we installed surface 
drainage to assist the drying. This had to be 
accomplished without drowning the laborers. 
Large sheets of waste galvanized iron roofing were 
thrown forward and heavy planks used to bridge 
the space between these sheets and put only 
light pressure on the thin crust. Shallow ditches 
were then dug by laborers standing on the planks. 
They do not prefer work of this nature! This 
preliminary ditch rapidly dries the soil at its sides 
so that it will bear a man's weight if he does not 
stay too long in one place, and it can then be made 
deeper. The process is repeated until the desired 
depth and grade are obtained. When the cracks 
do not become filled by the action of rains, as 
soon as the crust is sufficiently strong to support 
a mule, an iron rail is dragged over the surface, to 
level and fill the cracks. When the material 
contains much sand or gravel, the cracks do not 
form. 
About one half of the area on which Colon is 





■■ ■?=* 



Cracks in a hydraulic fill 



Attack by Filling 121 

built was filled by this hydraulic method at the 
request of the sanitary department and is now 
producing a revenue. The cost of this work at 
Colon was charged against the sanitary depart- 
ment, but the large ground rents accruing have 
not been placed to its credit. The extensive area 
on which the new town of Balboa is being built 
was formerly a tidal swamp. It was filled by 
dumping soil from Culebra Cut upon it. It 
was more expensive to dump waste in that 
locality than at other established dumps, where it 
would have served no purpose and had no future 
value. But the difference of cost of dumping 
was also charged against sanitation, although the 
sanitary department has not been credited with 
the rise in value of property formerly worthless. 

The work of filling the large swampy area north 
of Ancon will be similarly charged. Of course the 
paper cost of Isthmian sanitation is increased by 
these charges. After the hydraulic fills near 
settlements become thoroughly dry and receive 
the necessary surface drainage, the value of 
formerly useless property increases. 



CHAPTER IX 

ATTACK ON PROPAGATION AREAS BY DRAINAGE 
GENERAL CONSIDERATIONS 

\ X 71THOUT doubt, proper drainage is the all- 
" * important and most effective method of 
eliminating malaria. It should be more generally 
known that so far as mosquito eradication is con- 
cerned, the drainage scheme should be planned with 
a view to destroying them. The sanitarian and the 
engineer often look at the problem from different 
points of view. The sanitarian wishes to elimi- 
nate all Anopheles-propagation areas permanently. 
If that end cannot be obtained at a reasonable 
cost, to ensure success he plans a scheme of drain- 
age which would eliminate or reduce the possible 
breeding areas as much as possible, keep the annual 
maintenance expenses at the lowest figure, and 
eliminate to the utmost conditions favorable to 
mosquito development and the necessity for 
continuous future inspection of ditches. Any 

122 



Attack by Drainage 123 

scheme that prevents a possible failure due to 
improper or neglected inspection, or which 
abolishes the personal equation, is worthy of 
consideration. 

The engineer often has another point of view. 
He plans the ditches for rapid removal of storm 
water, but gives no thought to the condition of the 
ditch between showers, and seldom has any interest 
in or responsibility for the future success of the 
mosquito drainage work. The sanitary officer in 
charge may be replaced by a man inexperienced 
in Anopheles control. The engineer who planned 
the work may be in another part of the world and 
probably has not designed his drainage scheme to 
meet these conditions. In general, he tries to be 
rid of a body of standing water at the lowest first 
cost. To him the problem is very simple, and 
apparently not worth much consideration. He 
may not be interested in the habits of mosquitoes 
and is generally ignorant of the fact that small 
puddles or even a fraction of an inch of water left 
standing will defeat the sanitarian's object. He 
may not care if the water in the ditches runs 
rapidly enough to remove Anopheles larvae, but in 
the tropics the width of the bottom of a ditch often 
determines whether it is to be a means of reducing 
Anopheles or of producing an additional supply. 



124 The Control of Mosquitoes 

If a competent civil engineer devotes his entire 
attention to these matters, he not only makes a 
study of details affecting the problem, but will 
probably invent new methods of procedure and 
new short cuts. It is not unusual for an engineer 
to leave minor ditching work to the judgment of a 
gang foreman, who makes the ditches too wide, 
spoils the grades, and frequently the work is not 
only unsuccessful, but expensive to maintain, and 
ultimately becomes a dangerous source of Anoph- 
eles. It is possible for an improperly drained 
area to produce more mosquitoes after the ill- 
planned work is concluded, than before the drain- 
age was begun. 

An ideal scheme of drainage would be a plan to 
remove all standing water from the Anopheles- 
producing area, and take care of all storm water 
in such a manner that within a short period after 
a storm the ground surface and ditches would 
become dry. These conditions would eliminate 
Anopheles and many other species of troublesome 
mosquitoes. 

In many places in the tropics this ideal cannot 
be attained, because of such factors as geological 
formation, texture of surface soil and subsoil, 
topography, vegetation, the extent and distribu- 
tion of rainfall, and air movement. The mere fact 



Attack by Drainage 125 

that open ditches are not always followed by- 
perfect "Anopheles drainage" need not in any way 
discourage the sanitarian. He must overcome 
many apparently difficult problems, or his work 
will not be successful. Open ditches should be 
made as straight as possible, and have narrow 
bottoms. The side slopes should be clean cut. 

Drains with flat grades may often deteriorate 
to conditions that actually produce Anopheles. 
Sometimes it is difficult to prevent the formation of 
"pot-holes" in ditches on heavy grades, and as 
each foot of open ditch means an item of expense 
for maintenance, the drainage scheme should be 
planned to use the least total length of ditches. 
To attain the best results, we must be sure the 
drain is correctly located. There is often a choice 
of locations for a drainage ditch. The character 
of the surface soil may be such that the necessity 
for certain branch ditches is doubtful. When 
working in wet areas it is often best to locate and 
install the main ditches before the laterals are 
definitely located. This is especially true of 
extensive areas covered with water and jungle 
where the low places are not yet known, and their 
drainage can be planned better after the deep 
water has been removed. 

Additional advantages ensue in cases where 



126 The Control of Mosquitoes 

seepage water and springs complicate the problem. 
Where these conditions are found the use of the 
herring-bone type of ditch is often unsatisfactory, 
and the position of the branch ditches may depend 
to a large extent on the location of the seepage 
water and the points at which it comes to the 
surface, "seepage outcrops." 

A man who has had extensive practice in drain- 
age for anti-malaria purposes can do much of the 
minor detail work without supervision, but where 
grades are light and work extensive, it is essential 
to have levels taken, to profit by all the existing 
grade. If ground and relative elevations are 
judged by the eye alone, wrong conclusions may 
easily be drawn as to the possibilities of drainage, 
and it is too late, or at least more expensive, to cor- 
rect errors after the actual work is well advanced. 

It must be kept in mind that some swampy 
areas, for reasons not yet thoroughly understood, 
are not sources of Anopheles. In other cases they 
may be the source of non-malaria conveying 
species. Where possible, without increasing the 
cost of the drainage work, it is often advisable to 
determine the most prolific sources of the malaria- 
carrying Anopheles, and to give the drainage of 
these places preference over other work. 

Seasonal changes may affect the production of 



Attack by Drainage 127 

mosquitoes, and certain breeding grounds may be 
harmful only at one short period of the year, or 
only during the wettest part of an unusually rainy 
year. The latter condition calls for attention 
when Anopheles originate in water coming from 
seepage outcrops. 

Many problems on the Isthmus differ from those 
encountered in other parts of the tropics where 
mosquito eradication or control measures will be 
undertaken in the near future, and it may become 
necessary to modify Isthmian sanitary practice to 
attain results rapidly and economically in other 
localities. However, it is thought that an outline 
of difficulties encountered, and a brief account of 
the methods used to overcome them, may be of 
assistance to other communities suffering from 
malarial fever. 

OPEN DRAINS OR DITCHES 

This type of drain may be divided into two 
classes: First, those that are intended to carry off 
storm water during rainy periods, and becoming 
dry a day or two after the rain ceases, are known as 
storm-water drains. Secondly, those that carry 
off water for a period of more than a week, or 
which hold more or less water continuously. 

Some storm-water ditches may fall under the 



128 The Control of Mosquitoes 

second classification for varying periods of time 
during the wet season, depending upon the rain 
distribution in respect to time or continuity. 

Storm- water drains may fail to give satisfactory 
results because of a tendency of the bottom or 
sides to scour at times of heavy flow. The charac- 
ter of soil at the bottom and sides of the ditch de- 
termines its ability to remain standing with fixed 
cross-section. It should be remembered that at 
times of maximum rainfall the ditch water may 
carry large quantities of gravel and stones, which 
assist in causing more erosion than usual. Other 
conditions being equal, the steeper the grade of 
the ditch the greater will be the tendency to the 
scouring of the sides and bottom. Soft spots or 
places are often found along the line of the ditch 
where the texture of soil lends itself to erosion; 
and washouts may be expected at these points. 

Again, where the ditch becomes temporarily 
obstructed by stone or otherwise, excessive local 
scouring action may ensue, removing soil from 
below the grade line of the ditch bottom, and 
causing a hole in it. During subsequent storms 
one or more stones may collect in this depression, 
and travel with a circular grinding motion, that 
enlarges the hole. These cavities are known as 
pot-holes, and retain water long after the storm 



Attack by Drainage 129 

ditch is dry. In many cases these depressions may 
be filled with stone, well rammed into place and 
chinked, and the original grade of the ditch bottom 
reestablished before much harm is done. There is 
a tendency to neglect these holes, and to assume 
that the ditch is dry and does not need inspection. 
This assumption would result in Anopheles pro- 
duction in the depressions below the ditch grade 
line. 

When ditches contain water continuously, or 
for periods long enough to bring Anopheles larvae 
to full development, they must receive regular 
weekly inspection. During the part of the year 
when large volumes of water pass off in short 
periods, the ditches are generally swept free of 
mosquito larvae. When the average flow is fairly 
rapid, the same effect is produced. 

It is when the velocity of the water becomes 
retarded that conditions become most favorable 
to mosquito development. In open ditches having 
a rather flat grade such conditions often prevail, 
and vegetation within them may develop rapidly. 
Both grass and aquatic vegetation assist in re- 
tarding the stream flow, besides furnishing food 
and hiding-places for mosquito larvae. The retard- 
ing of the current causes silt to deposit and this 
affords sufficient plant food to make vegetation 



130 The Control of Mosquitoes 

grow rapidly, and also raises the grade of the ditch 
bottom. 

Ditches in soft soil and having a low grade are 
the most expensive to maintain, and may become 
a prolific source of Anopheles. Vegetation on the 
sloping sides of open ditches prevents the banks 
from scouring, but when the grass grows long it 
falls into the water, retards the current, and often 
assists in making conditions favorable to mosquito 
propagation. Streams and ditches are treated 
similarly; by straightening the channel and re- 
grading parts of the bottom, we confine the normal 
water flow and increase its velocity, which removes 
the hiding-places of larvae. 

TILE DRAINS 

When rock, hard-pan, or other impervious 
material underlies the surface soil, the ground 
water not being able to penetrate it follows down- 
hill on its upper surface, and where the impervious 
stratum comes to the surface of the ground or 
close to it, there may be a source of water. When 
small quantities of water appear in this way on the 
ground surface, they are called ' ' seepage outcrops." 
The line where water seeps out of the ground may 
be short, or may extend along the entire side of a 
hill, and become the source of a hillside swampy 



Attack by Drainage 



131 



area. The extent of the seepage outcrop line 
may vary with the duration of a rainy season. 
Some seepage outcrops may be permanent, others 
intermittent, and yet others may be active only 
for a short time, during periods of excessive rain, 
and may not become active every year. 

The character of the surface soil below the 




niuiniiunuii 
Longitudinal Section 
Intercepting Tile Drain 



Orosa Section 

Intercepting 

Tile Drain. 

Longitudinal section and cross section of intercepting tile 

drain. 



seepage area may vary. If more or less imper- 
vious, water remains on the ground surface, and 
Anopheles are produced. In places where seepage 
water is commonly found, it is well to examine all 
sharp changes of grade in surface topography, and 
the ground near the toes of abrupt slopes. As the 
rainy season advances, the line of seepage outcrop 
often moves up the slope, and in controlling this 
water the highest points of the outcrop must be 
determined. Under the conditions existing at 
Panama it was found best, as a general rule, to 



132 The Control of Mosquitoes 

control seepage water outcrops by tile drainage, 
with a minimum grade limit of one foot in two 
hundred. The plan adopted is to intercept the 
seepage water by tile drains placed approximately 
at right angles to the line of flow of seepage water. 

The line of seepage outcrop is determined 
during the wet season, when the seepage is most 
pronounced, and levels taken with an instrument. 
The proposed ditch to take the tile drain is staked 
in the field, and a profile map made. The profile, 
compared to surface conditions, will show any 
changes that can be made with advantage, and at 
times it is essential to try out several lines in order 
to obtain the best and most economical location 
for the tile drain. When the uphill portion of the 
tile line had a long steep grade, no harm was done 
by using a flatter grade for a short length toward 
the outlet, as the excessive rains in Panama 
caused the pipes to run full section or nearly so. 

The tile ditches are made as narrow as conven- 
ient, and their bottoms are kept at the established 
grade. The openings left between the successive 
tile lengths are from one eighth to one quarter of 
an inch, and the joints are not wrapped with 
muslin or covered in any way. If soft spots are 
found in the bottom of the trench, stones are 
rammed into place until a solid foundation is 



Attack by Drainage 133 

obtained. After the tile is wedged securely in 
place the trench is filled with stone to the height 
of a few inches above the original ground surface. 
Earth excavated is placed only on the downhill side 
of the excavation. Small stone is preferable for 
the top layer of cover stone at the ground surface. 
This scheme of drainage has given excellent 
results. 

There are conditions under which intercepting 
tile drainage should not be used. If unforeseen 
future changes of topography produce these con- 
ditions, the tile line will probably operate in an 
unsatisfactory manner. The soil over the greater 
part of the Isthmus contains a large percentage of 
clay. If the lands above the tile line are kept 
covered with vegetation or left in their natural 
condition, the surface water running down the 
hillsides is not heavily charged with clay and silt, 
and passes through the cover stone above the tile 
line and then off through the tile. Should the soil 
be bared or excavated above the tile line, or a hillside 
road located across the tile line, large quantities of 
impervious material will be washed onto the cover 
stone, and fill up all the spaces between the stones, 
and no water can reach the tile. Tile drains are 
not planned to meet these conditions, and cannot 
operate under them without costly maintenance. 



134 The Control of Mosquitoes 

Under normal conditions the subsurface drainage 
systems cost practically nothing to maintain. 
Many of the drains installed seven years ago have 
received no attention whatever since they were laid, 
and are doing their work now as well as when new. 
Anopheles are not produced in subsurface drains. 

A few essential points to be kept in mind for 
intercepting tile drainage for Anopheles eradication 
are as follows: No water should be allowed to 
enter the upper end of the tile drain or of its 
branches. The grade of the trench bottom should 
be true; tiles must not be located on soft mud, 
where they may sink. Where the tile line comes 
near the surface, due to topographical variations, 
proper bridge crossings must be made, so that 
wagons will not pass over and crush the tile. 
Greasy water and house waste must not be 
allowed to discharge into any part of the tile line 
system. If drainage from roadside ditches or 
excavated areas is turned onto the cover stone, a 
tile line will probably become useless. 

The profile of a proposed line will indicate the 
amount of material to be excavated, and the depth 
of the trench. It may often be advisable to use 
one or more branch lines to include all the seepage 
water, as the cost of excavation and cover stone 
may be less than that of a single deep ditch. 



Attack by Drainage 



i35 



The outlet or point of discharge of a tile drain 
must be well above the ground surface or above 
the body of water onto which it is to discharge its 
contents. Much solid matter is transported 
through the pipe, and may in time block the outlet 
at the point of discharge. This condition might 





"Wall at Outlet of Tile 
Drain 



fZ~XZ| Cross Section of Outlet 
of Tile Drain 



Detail of outlet of a tile drain. 



result in the clogging of a part, or all of the line. 
It is well to arrange for periodical inspection of all 
outlets, especially where the lower end of the tile 
line has a relatively low grade. 

Branch lines should be connected to the main 
line by means of Y joints and approach it at an 
acute angle or on a curve. Water-bearing strata 
may be deep enough to necessitate the installation 
of several parallel branch lines placed to prevent 
seepage water outcrop between the lines of tile. 



136 The Control of Mosquitoes 



Where seepage outcrops on bare hillsides, or at 
the foot of slopes where there is insufficient grade 
for the use of tile drains, open ditches are used. 
In these cases the water is intercepted as in the 




.Side View 

Junction of Two 

Tile Lines showing 

"Y Joint" and Grades* 



Y Joint 



Plan of Junction 
of Tile Lines. 




Plan and side view of junction of tile lines. 

case of a tile ditch, but the side of the ditch nearest 
the hill must be given flatter slope than the other 
side, because it is wet and more apt to break off and 
fall into the ditch. If such a ditch is expensive to 
maintain, it should be lined with concrete, and 
plenty of weep holes left to care for seepage 
water. 



Attack by Drainage 137 

PERMANENT LINING OF DITCHES 

The method that is most economical and durable 
for any special locality should be used. It is often 
more economical in the long run to line ditches 
with stone or concrete in permanent villages and 
suburbs of towns. A ditch may be properly 
shaped and roughly lined with field stones, and the 
bottom finished with cement mortar. If a flat V- 
shaped section is used, it is found best to round off 
the bottom, so that obstructions will not remain in 
the ditch and collect other debris. Elaborate 
or very smooth finish for ditches is not essential. 

It may be thought more economical to maintain 
open ditches than to line them, and in this case the 
actual cost of maintenance, including cleaning, 
regrading, and oiling treatment, should be accu- 
rately kept. If one or more ditches are lined, a 
true comparison of cost of the open ditch versus 
the lined ditch can be made. 

Experience on the Isthmus has indicated that in 
most cases it is better to line permanent small 
ditches which would otherwise have to receive 
treatment throughout the year. Before lining a 
ditch an estimate of cost of lining was obtained, 
and compared with the estimated cost of mainten- 
ance and treatment necessary for the unlined ditch. 



138 The Control of Mosquitoes 

In some cases lime mortar and rough stone have 
been used to advantage, with a small amount of 
cement mortar for a finishing surface, or the bottom 
was lined with flat stone, the interspaces chinked 
with small stone and sealed with cement mortar. 
Where it was necessary to line the bottom of the 
ditch only, the sides were given a slope beyond 
the angle of repose, and allowed to become 
covered with grass. As stone is sometimes costly, 
the quantity used should be reduced to a minimum. 

REINFORCED CONCRETE LINING FOR DITCHES 

Where broken stone "screenings' ' or gravel can 
be obtained at a reasonable rate, a reinforced 
concrete ditch of light section may be the best 
method of ditch lining. In the Canal Zone, a 
thickness of about two inches is used for small 
ditches with two-inch mesh hexagonal poultry 
netting for reinforcing. In one case where a steep 
embankment slid, a section of seven feet of this 
lining was lifted out in one piece. It was only 
necessary to regrade the ditch and replace the 
section where it belonged. With most ditches it is 
sufficient to line the bottoms and a few inches up 
each side, as we are interested in the flow line of 
the stream only after the rain has ceased. 

Work of this nature cost about twelve cents per 




n3 
C 

o 



i=. -I- 3 



o 



IS 

*d 
o 



0) 







*d 






d 
o 
U 



Attack by Drainage 



i39 



linear foot, in place, for ditches a foot wide, with 
unsatisfactory labor costing ten cents per hour. 
Reinforced concrete lining should be selected for 




Cross Section 
of Key Wall 



Weep Hole 



Plan of Key Wall 
-'Concrete Lining of Ditch 



-Key Wall 



Plan and cross section of key wall and position of weep 

holes. 



ditches near permanent settlements that are 
possible mosquito producers throughout the 
greater part of the year. The work should be 
accomplished during the dry season, and the ditch 



140 The Control of Mosquitoes 

water temporarily diverted until the concrete has 
set. A thin layer of concrete about one inch thick 
should be laid on the prepared ditch bottom, the 



Retaining Wall 

used at Sharp 

Curve of Concrete 

Lined Ditch 



Retaining Wall 




Key Walls used at 

Outside Edge of Sharp 

Curve of Concrete 

Lined Ditch 

To Prevent Storm Water 

Leaving Ditch 



To prevent water leaving lined ditches at bends or sharp 
curves, key walls are used to break the current, or 
the outside wall is made higher. 

wire mesh pinned down on it, and the second layer 
of concrete installed, leaving the wire mesh 
embedded in the concrete. River gravel is as good 
as broken stone or screenings and sand for this 
purpose. In larger ditches the sides are sloped, 
and lined for about a foot above the floor line. 




Concrete ditch lining 




Concrete-lined ditch at Balboa 



Attack by Drainage 



141 



When natural watercourses are treated in this 
way advantageous realignment is first made; and 
grades are used that fit the topography; in many 
cases causing the actual length of the stream to be 
considerably shortened, and its velocity increased. 

Whenever ditches are lined, sufficient weep holes 




Junction of Branch Ditch 
and Main Ditch 



Branch ditches should join main ditches at an 
acute angle or on a curve. 

must be installed to enable the water that follows 
the sides of the concrete lining to enter the ditch. 
When weep holes are omitted water is apt to stay 
in puddles near the stone lining. Water has a 
tendency to flow along the side walls and under 
lined ditches. In many instances this is sufficient 
to tear away the earth supporting the ditch sides 
and at times even to undermine the lining. This 
action is prevented by installing key walls at right 



142 The Control of Mosquitoes 

angles to the axis of the ditch at necessary inter- 
vals. Weep holes are placed in the side walls on the 
upstream side of the key wall, and, if necessary, 
the key wall can be carried up to the level of the 
top of the ditch or above it. These walls act as a 
barrier in time of freshets and break the rapid 
current that would otherwise tear away the earth 
banks and make pockets immediately outside the 




Concrete Lining 
in Ditch Bottom 



Concrete lining for bottom of small ditch. 

ditch lining. On heavy grades it is necessary for 
the key walls to extend about a foot below the 
ditch bottom and under the ditch floor, extending 
well into each bank. 

Where weep holes fail to operate because of 
becoming clogged with impervious material, 
broken stone can be used to replace the clay near 
the weep hole. They should always point down- 
ward toward the center line of the ditch, or else in 
extreme dry seasons they become mosquito breed- 
ing places. 




Junction of concrete ditches, showing splash wall to confine 
water within the ditch 



Attack by Drainage 



143 



Where sharp bends or curves occur in lined 
ditches, and especially on heavy grades, provision 
must be made to prevent storm water climbing 
out of the ditch, and undermining a considerable 
section of the lining. This is easily arranged by 
introducing one or more key walls on the outer 
side of the curve, widening the ditch near the 
point of curvature, or by raising the outer wall in 





Concrete Lining 

Eeinforcing Wire 



.Eeinf orced Concrete Lining 



plash Wall 

I Cross Section 

Showing 

Junction of 

Concrete 

I Lined DLtch 

land A Branch 

Ditch 



Junction of branch ditch with a lined ditch. 

the vicinity of the point of curvature. In small 
ditches the same result is obtained by decreasing 
the slope of the outer wall, or making it vertical 
near the point of curvature. 

It is not advisable to have a branch ditch meet a 
larger ditch and be at right angles to it. It is 
better to curve the small ditch near the junction 
of the two so that they meet in a Y joint. If this 
is not done, much vegetable debris, mud, and stone 
may be deposited in the smaller ditch. It is well 
to make the main ditch somewhat wider at junc- 
tion points, sharp bends, and points of curvature. 



144 The Control of Mosquitoes 

In wide ditches the stone or concrete floor lining 
should slope toward the center. 

MAINTENANCE OF DITCHES 

Maintenance of a ditch implies keeping it in 
a condition to carry off water and not produce 
mosquitoes. The work in Panama consisted of 
keeping the bottom to proper grade, the cross 
section of uniform width, the removal of all ob- 
structions that affected the velocity of the water, 
and also vegetable growth and algae that furnished 
food and protection for the larvae. It included 
treating the ditch with oil and other forms of 
larvacide when necessary to destroy larvae, and 
periodical inspection to make sure that the ditch 
was in satisfactory condition and free from mos- 
quito larvae. 

In comparing an open earth ditch with a con- 
crete lined one, we found the following advantages 
in favor of the lined ditch : The velocity of water is 
increased to such an extent that mosquito larvae 
cannot live in it but are washed away or destroyed. 
The increased velocity prevents the deposit of silt, 
etc. Each shower cleans the ditch out, and gen- 
erally removes any debris that has collected. The 
cross section of the ditch remains uniform. No 
grass or other vegetation clogs the ditch. Algae 




Burning grass from side of ditch ; crude oil used as fuel 



Attack by Drainage 145 

only occurs in lined ditches having practically no 
grade, and then only at periods of minimum flow. 
It is rapidly removed by the application of a small 
quantity of copper sulphate used at the head of 
the ditch. Food and protection for Anopheles 
larvae are absent, and they appear to avoid in- 
stinctively ovipositing in places where these 
conditions prevail. 

On fair grades there is no necessity for oiling or 
treatment of a lined ditch. Inspection may be 
made less often and as rapidly as one can walk. 
Defects may be noted at a glance. If the lining 
has been properly planned and installed, there is 
but little maintenance cost, and in most cases 
none at all. 

Where ditches are practically without grade, 
and the soil in the higher lands above the ditch is 
heavily eroded by storm water, as the velocity 
decreases, the depositing of matter in suspension 
increases, but generally only a fraction of the 
amount is deposited in a lined ditch that remains 
in an open earth ditch. In fact, concrete lined 
ditches often take care of themselves, and they 
need very little attention. 

The disadvantage of concrete lined ditches is 
the higher first cost, and in case of construction 
work, where the topography is being constantly 



10 



146 The Control of Mosquitoes 

changed, it is not advisable to install permanent 
work that must soon be destroyed or covered up. 

Under the conditions existing on the Isthmus, 
the proper maintenance of open ditches is often a 
difficult task. It is necessary at all times to keep 
them free from obstructions. Even a small twig 
caught by an irregularity on the bank will cause 
other matter to collect and form a temporary 
dam. When this happens in a ditch of low grade, 
it may result in the deposit of silt, sand, and clay 
for one or several hundred yards above the 
obstruction. 

In a deep ditch regrading and cleaning are 
expensive. The current velocity may be increased 
on the side of the ditch opposite an obstruction, 
undermining that bank completely, and deposit- 
ing large amounts of material at points lower down. 

Where a ditch passes through soft material, the 
channel frequently becomes out of alignment, and 
constant cleaning and regrading tends to widen it. 
During dry periods it may develop into a semi- 
stagnant pool, in which algae forms rapidly, making 
a new small temporary ditch necessary within the 
larger one. The small one has a tendency to close 
up, and is often destroyed by the first shower. If 
cattle walk in the ditch, the water in each hoof- 
print must be separately oiled. In general, as the 




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Attack by Drainage 147 

dry season advances, the cross section of the 
wetted portion of a ditch grows smaller, and little 
puddles capable of mosquito production are left 
in the stream bed detached from the oiled water 
in motion. All these depressions must be sepa- 
rately oiled, and only an intelligent and inter- 
ested laborer can be trusted to do this. As the 
quantity of ditch water decreases, the rate of 
growth of vegetation increases, and it is then nec- 
essary to remove it, or smear it thickly with oil to 
leave the film free from air holes. Then the work 
must be thoroughly inspected to see that it 
has been properly accomplished. A sudden show- 
er may remove all the oil and the work have to 
be repeated. 

When the grade becomes flat by removing the 
vegetation, the ditch may gradually change into 
a long stagnant pool, and the advantage gained by 
velocity is lost. It can readily be seen how im- 
portant it is to have for foreman in charge of the 
ditching maintenance gang a man who knows the 
necessity of working correctly, and who can be 
held responsible for results. 

Spoiling the grade of ditches causes more costly 
future oiling and ditch maintenance. Ditches 
and streams should have a uniform grade, and as 
straight a course as local conditions permit. Least 



148 The Control of Mosquitoes 

larvae will be found where steep banks stretch 
above and below the normal flow line. The width 
of ditches should be no more than is absolutely- 
essential, and the water in them should be kept in 
motion. Prompt removal of obstructions and 
attention to minor detail save much future ex- 
penditure and reduce propagation. Laborers at 
work cleaning or regrading a ditch frequently pile 
the excavated mud in such a manner that sooner 
or later it returns to its original position. This 
practice is common along railroads, and laborers 
should be closely watched to prevent it. 

Ditch maintenance gangs often make ditches 
wider and deeper. On hillsides the banks of ditches 
are apt to collapse from constant deepening of flood 
water. This can be partially controlled by giving 
a proper slope to the ditch sides, allowing grass to 
grow on them, and preventing holes forming in the 
bottom of the ditch. As soon as the soft spots are 
formed, they must be filled with stone, thoroughly 
tamped into place. When it is definitely known 
that the erosion cannot be stopped, and that the 
material carried away will be deposited in the 
ditch at a point lower downstream, to be removed 
at regular intervals, an estimate should be made 
of the cost of constant removal compared with the 
expense of lining the parts of the ditch being 




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Attack by Drainage 149 

washed away. The grades of pipe lines conveying 
ditch water under roads or buildings should be 
slightly more than that of the ditch leading to 
them. Their entrances should be screened to 
prevent debris entering the pipe without causing 
water to be impounded above the pipe at time of 
floods. A stone or board floor, or apron, at the pipe 
outlet will prevent erosion. 

The stability of open ditches and the cost of 
keeping them to true grade and uniform cross 
section with freedom from larvae depends upon the 
following factors: 

Character of the soil. 

Frequency of heavy rainfall. 

Grade of the ditch bottom. 

Change of grade with corresponding deposit of 

material carried in flood time. 
Presence of seepage water in banks of ditch. 
Natural angle of repose of ditch banks when wet. 
Presence or absence of vegetable matter washed 

downstream. 
Absence or presence of grass on the banks. 

Natural watercourses are classified as ditches, 
and have to be trained to keep the water at maxi- 
mum velocity during dry periods. 

The question of uniform cross section of ditches 
has already been referred to, and variations of 
width in a body of flowing water may not only 



150 The Control of Mosquitoes 

cause silt, etc., to be deposited, but decreases the 
surface velocity near the banks in the wider section, 
and in such places algae will grow and mosquito 
larvae thrive. Near Empire the topography was 
suitable for the temporary impounding of water, 
and by placing a gate at the entrance to a culvert, 
sufficient water was obtained to thoroughly flush 
the ditch below it and remove all mosquito larvae 
whenever desired. 







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CHAPTER X 

ATTACK ON PROPAGATION AREAS BY OILING 

UNDER unfavorable conditions larvae will prob- 
ably be found in various bodies of water 
notwithstanding all that may be done by filling and 
drainage to reduce to a minimum the areas favor- 
able for breeding, and if they are to be prevented 
from maturing into adults some other method of 
destruction must be adopted. Oil is the most 
commonly used larvacide, and being generally 
applicable is the most useful. Kerosene, crude 
oils of paraffin and of asphaltum base, and the 
various distillates have been used, and also crude 
creosote, eucalyptus, and juniper oil. z 

Just how oil kills mosquito larvae and pupae, the 
writers are not prepared to assert. The generally^ 
accepted theory is that oil clogs the breathing 
tubes of the larvae and pupae. Another theory is 
that by reducing the surface tension, the oil film 
makes it difficult, if not impossible, for the larvae 

1 See Ross on the Prevention of Malaria. 

151 



152 The Control of Mosquitoes 

to hold themselves at the surface. Possibly a 
combination of three causes kills the larvae : 

i. Specific toxicity of the oil to the larvae and 
pupae. 

2. Minute particles of oil clogging the breath- 
ing tube. 

3. Reduction of surface tension, making it 
difficult for the larvae to remain long enough at the 
surface to make a rupture in the oil film and thus 
obtain air. 

Oil appears to be toxic to mosquito larvae. We 
have observed that a number of larvae die shortly 
after coming in contact with it. Mere deprivation 
of air does not cause death very rapidly in mos- 
quito larvae. In submerged cages the larvae and 
pupae of Anopheles often survive more than an 
hour. 

Probably the minute particles of oil find their 
way into the breathing tubes, and cause death by 
clogging. We have seen larvae take their breathing 
tubes into their mouths after the contact with 
the oil and apparently make frantic endeavors to 
remove some offending substance. 

The decrease in surface tension is also a factor, 
although its importance varies with the various 
genera of mosquitoes. The Aedes calopus can 
remain at the bottom of a water vessel for a long 



Attack by Oiling 153 

time; the Anopheles larvae remain on the surface of 
the water unless frightened, and are more rapidly 
killed by the oil film than others. 

There is little, if any, ovipositing by mosquitoes 
on water heavily treated with oil. 

Kerosene has its merits. Its especial desir- 
ability is its property of rapidly forming a thin 
film. It was tried in Panama, but rejected in 
favor of crude oil. The objections to its use are : 

1. The film is so thin that very slight disturb- 
ances of the water surface, by flotsam, vegetation 
projecting through the surface of the water, ripples 
caused by wind or current, etc., break the con- 
tinuity of the film. 

2. Kerosene is expensive. 

3. It is transparent, and is wasted by oilers 
because it is difficult to see where the film is 
satisfactory. 

4. Liability to fire, where sparks may drop 
into it ; for instance, near a railroad. 

Crude oil of asphaltum base is used extensively 
in Panama. Its great advantage is its low cost, 
and because of that, its poor spreading qualities and 
high specific gravity may be overlooked in a warm 
country. We doubt if the quality of oil used in 
Panama would serve in a cooler country during 
spring and fall months. The oil delivered in 



154 The Control of Mosquitoes 

Panama is imported from California. It averages 
20° Baume. Oil from the same source, testing 
30 Baume, was much more satisfactory, but only 
a limited amount could be obtained. The crude 
oil was mixed with kerosene in varying propor- 
tions to increase its spreading qualities, but the 
resulting mixture proved more expensive and less 
effective for practical field work than treating this 
particular grade of oil with larvacide which con- 
tained phenol compounds. It is possible that some 
other grades of relatively heavy oils may be more 
advantageously used after mixing them with 
kerosene, when its cost is not excessive. 

METHODS OF APPLICATION 

The methods of applying oil for larvacidal 
purposes may be classified as continuous or inter- 
mittent. 

The most serviceable for continuous effect is the 
"drip method" in which drops of oil fall upon the 
surface of the water from a specially designed 
container with sufficient frequency and in such a 
manner as to form a continuous thin film of oil 
over a certain area of water. This layer of oil is 
usually known as the ' ' oil film. ' ' 

"Drips" are used advantageously where there 
is a moderate surface current, where the water 



Attack by Oiling 155 

surface flows smoothly, where the channel is fairly 
free from obstructions and flotsam, and where 
there is very little vegetation and algae. In a word 
" drips " are most useful where there are few, if any, 
impediments to the formation of a good unbroken 
film. An important advantage gained by using 
oil drips is that oil is transported by the stream, 
and left in the form of an oil film on the quiet 
water along the bank where there is little or no 
current, and where mosquito larvae are most apt to 
be found. 

Circumstances occasionally arise which call for 
the installation of a drip on a stream that does not 
offer the requirements mentioned. For instance, a 
rapidly moving, tortuous stream may empty into 
a quiet, wide pond, in which conditions are favor- 
able to mosquito breeding. This stream may flow 
close to a road along which oil may be easily 
transported. The pond may be at an inconvenient 
distance from the road, and difficult of access for 
wagon or cart. Under these circumstances, it may 
be advisable to install a drip on the stream at some 
point near the road, and by this means carry the 
oil to the pond, where it is needed. This example 
shows the possibilities of utilizing a stream as an 
oil carrier. Our construction camps were fre- 
quently situated near sluggish streams or branches 



156 The Control of Mosquitoes 

of rivers. Hillside streams from distant hills 
joined the quieter water near the camp. Larvae 
and pupae were frequently carried by storm water 
toward the settlement and remained to develop 
in the quieter water in its vicinity. A rainstorm 
thus produced a sudden influx of mosquitoes at 
the settlement. This was prevented by installing 
oil drips on all streams flowing toward settlements. 
The drip may be used on temporary lagoons, as 
an auxiliary to intermittent treatment. In the 
rainy season in Panama lagoons are formed in 
certain depressions from which drainage is difficult. 
These lagoons rise and fall several feet in a few 
days. Each fall of the water surface causes the 
deposit of a large quantity of oil upon the banks, 
where it is soon absorbed by the soil. After every 
fall the oil film on the lagoon may have to be 
restored by reapplication. This is, of course, a 
great waste of labor and material. In many 
instances labor and oil can be saved in such places 
by introducing a few crude rafts carrying drips 
and moored at suitable intervals in such a way 
that they will readily rise and fall with the move- 
ment of the water, and yet remain in about the 
same position on the lagoon. The drips auto- 
matically maintain the desired oil film, and are 
replenished from time to time from a punt or boat. 



Attack by Oiling 157 

Breeding places for mosquitoes have been found 
in catch basins of sewers, particularly during long 
intervals between rains. This condition has been 
remedied by small drips, but it would be better 
to use a device making it impossible for mosquitoes 
to enter catch basins except at the time water 
flows into the basin. 

The measure of success in the operation of a drip 
is that it shall work as nearly automatically as 
possible. The ideal drip is one that, once adjusted, 
requires no further attention except refilling. With 
heavy oil, the ideal has not been attained in 
Panama. We were compelled to use drips that 
worked in a fairly satisfactory manner. Although 
far from perfection, the drips were extremely 
useful. 

The difficulties encountered in devising a satis- 
factory drip are: 

That crude oil is too thick to permit of making 
use of capillary attraction, as may be done with 
kerosene and light oils. 

It contains a large quantity of suspended solids, 
which in time block a small hole or wick, and the 
flow either stops altogether, or is greatly impeded. 

The oil becomes more viscid in the cooler 
temperature of the night, and may stop flowing 
until it is warmed later in the morning. 



158 The Control of Mosquitoes 

These difficulties have been partially overcome 
by using the following drips : 

The simplest form of drip is a vessel with a small 
hole punched in the bottom. This form is still 
much used in places where the installation is 
temporary, as on temporary ditches that are wet 




Cotton 
Bottom of Oil Can 



Oil Drip made by 

Inserting Nail in 

Bottom of Container 



A simple form of oil drip. 



for relatively short periods, small pools shortly to 
be drained, etc. A five-gallon kerosene can is 
commonly used, having a hole punched in it by a 
nail. A small quantity of cotton waste is wound 
around the nail just below its head. The nail is 
then pushed through the small hole from the inside 
of the can. The quantity of oil allowed to drip 
through the opening is regulated by pushing the 
nail point upward or pulling the nail downward. 



Attack by Oiling 159 

Barrels fitted with various adjustable spigots 
are also used, and work fairly well. The ordinary 
wooden spigot serves for barrels located on the 
larger streams. 

On the whole, perhaps the most satisfactory 
drip is one made of a standard garbage can of 
thirty gallons capacity. A slot % inch by \yi. 
inch is cut in the side of the can about five inches 
from the bottom. Into this slot a flat spout about 
three inches long is soldered, and an ordinary lamp 
wick inserted and made to project inside and out- 
side the spout. 

Water is poured into the bottom of the can 
until it reaches within an inch of the flat spout. 
Oil is then slowly poured in after previous mixing 
with about five per cent, by volume of larvacide, 
the latter thinning the oil. The amount of oil 
flowing from the can is regulated by compressing 
or prying open the spout until the drip gives the 
desired number of drops of oil per minute. 

In order to spread, the drops of heavy oil must 
strike the water surface with considerable force, 
hence it is best to elevate the drip so that the oil 
drops at least three feet before striking the surface 
of the water. On streams having an average width 
of one to two feet, from ten to twenty drops of 
oil per minute are applied. The quantity of oil 



i6o The Control of Mosquitoes 




Oil Can -used to 
Drip Light Oils. 




lUat "Lamp Wick 




Wick Holder 

L 



Detail of Drip 
.used for. Heavy Oils 




* Oil Drip for Heavy Oils 



Oil Drip Can Support 



The flat lamp wick drip for heavy oils. 



Attack by Oiling 161 

required depends upon the spread of the oil, the 
alignment of the stream, roughness of banks, grade, 
algae present, obstructions, etc. For economic 
control a trial should be made at each ditch or 
stream where a drip is used to determine the re- 
quisite rate of flow. In many cases the drip need 
only be operated continuously for one or two days 
a week. On long streams or ditches it was some- 
times necessary to use several drip cans, so placed 
that where the effect of the drip at the source of 
water ceased, the next drip was installed. Settled 
dry weather may permit the discontinuance of 
some drips and allow their location to be changed. 
The isolated pools remaining in the drying stream 
bed were treated by using knapsack sprayers. 

In practice it was found that drips required 
periodic attention. Each drip should be visited 
and adjusted at least twice a week; when new, 
three or four times a week. Even the best designed 
drip has required this periodic attention. 

Occasionally it may be necessary to install drips 
on streams subject to freshets. On such streams 
they should be secured to prevent their being 
carried off by a flood. 

Another way to obtain a continuous application 
of oil is to use cotton waste impregnated with it. 
This method has a limited field of application, but 



ii 



162 The Control of Mosquitoes 

may occasionally be used with advantage. Dis- 
carded oil- soaked cotton waste is tied into small 
bundles, immersed in crude oil, and then placed in 
small seepage streams and outcrops. If there is 
danger of its being washed away, it can be tied to a 
stone. These oil-soaked bundles of waste give a 
thin film of oil to the water passing by or under- 
neath them during seven to ten days. They may 
be resoaked in oil and used many times. This 
method of oiling is used where the volume of water 
is insufficient to warrant the use of a drip can. 
Other uses may suggest themselves under varying 
local conditions. 

As the conditions under which continuous oiling 
can be successfully carried out are rather limited, 
it follows that the larger part of oil application to 
mosquito breeding areas must be done by the 
periodical application of oil or " intermittent 
method.' ' 

In the intermittent method the aim is to produce 
a continuous film, and to retain it in place suffi- 
ciently long to kill all larvae in the water covered 
by the oil film. Given a perfect film, it must 
remain unbroken at least several hours to insure 
a marked reduction in the larvae under it. In- 
tentionally we do not say "destruction of all the 
larvae under the film," because in the tropics it is 




Oil drip applied to hillside stream 



Attack by Oiling 163 

not always possible, in the field, to produce and 
maintain an oil film on a large body of water at 
reasonable cost that will insure the death of all the 
larvae under the film. We have found Culex 
larvae under an apparently good oil film that had 
been in place several days in succession. The 
explanation may be found in the fact that the oil 
film, in the field, is frequently not continuous, and 
that defective places may be found in it by which 
the larvae and pupae obtain air. However, a very 
great reduction in the larvae may be achieved by 
proper oiling, and Anopheles larvae succumb much 
more rapidly than the Culex. 

The question of how frequently the oil must be 
applied, can be answered only after a knowledge 
of local conditions has been acquired. The rule is 
to oil at least once within the minimum of time 
required to mature an egg into an adult. In the 
Canal Zone for the mosquitoes most frequently 
encountered, this period is about eight days, and 
oil was therefore applied weekly. 

In the intermittent method enough oil must be 
applied to produce a continuous film, heavy enough 
to withstand the tearing action of small ripples, 
and the light flotsam and vegetation projecting 
through it. 

It is difficult, if not impossible, to say just how 



1 64 The Control of Mosquitoes 

much oil must be applied to a given area of water 
surface. Such an estimate may be made for 
laboratory work, but it cannot be made for success- 
ful field application. Many factors operate to 
make such an estimate difficult : Wind and wave 
action; presence of vegetation, grass and brush 
projecting through the water surface or floating on 
it, and algae; the varying density of the heavier oils, 
the diverse quality of various lots, and the varia- 
tions in a given lot under differences in tempera- 
ture. In Panama just enough is applied to attain 
the desired result. 

Where large quantities of oil are to be used, the 
first consideration, from a standpoint of economy, 
is the distribution of the oil from its source to the 
places where it is to be used. The following meth- 
ods of distribution were used in Panama. 

About 600,000 gallons of crude oil have been 
used annually for the sanitary work in the Canal 
Zone. The oil was brought from California in 
tank steamers, principally for use as fuel, and the 
supply for sanitary purposes was obtained from the 
oil company. The oil steamers discharged their 
cargo into storage tanks situated at the Pacific 
Ocean canal terminus. From these tanks it was 
pumped across the Isthmus of Panama through 
pipes owned by the oil company. At various 




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Attack by Oiling 165 

points on the Isthmus this oil main was tapped, 
and smaller storage tanks connected with it. 
Part of the oil used was obtained from the storage 
tanks at various places along the line, either 
directly, or by running small branch pipe lines 
from these tanks to smaller ones nearer the areas 
where the oil was to be applied. Part of the oil 
supply was transported in two railroad tank cars 
to places where connections could not be economi- 
cally made with the trans-isthmian oil line. These 
tank cars were filled at the Pacific storage tanks, 
and discharged their cargo into small tanks at 
various points. The aim was to have the tanks as 
near the ultimate destination of the oil as possible, 
but an adjacent location was sometimes imprac- 
ticable, because of the absence of railroad and road 
facilities. The tanks were properly covered, their 
faucets kept locked, and sand was piled near them 
for fire protection purposes. 

From the small tanks the oil was transported to 
the points where it was to be applied, through 
pipes, in mule-drawn tank carts, in canisters, on 
mule back, or rolled in drums or barrels. Where 
none of the above methods was feasible, it was 
carried by hand, or on the backs of laborers. 

The Isthmian topographical conditions fre- 
quently raised the cost of transportation and 



1 66 The Control of Mosquitoes 

application to several times the initial value of the 
oil. 

Heavy oils are best applied to water in the 
form of a stream or spray. When applied in this 
manner, the tendency to form a film is much 
greater. A number of pumps on the market are 
entirely satisfactory for this purpose. The pump 
found most satisfactory in the Canal Zone was 
called a "barrel pump" and was especially strong. 
The smaller types of hand boiler-pumps are also 
serviceable. The requisites of a good pump for 
heavy oils are simplicity and strength of construc- 
tion, and valves without rubber. 

It will be found occasionally that the heavier 
fuel oils, those below 25 Baume, are too thick for 
the pumps ordinarily used. These oils may be 
thinned by adding kerosene, two per cent, by 
volume of crude carbolic acid, or five per cent, of 
the "larvacide" described in this chapter. Other 
compounds of a character similar to the "lar- 
vacide" can also be used. 

A "knapsack sprayer" of the type used for 
spraying in orchards has given satisfactory ser- 
vice. This knapsack is made of heavy galvanized 
steel, or of copper; it contains a small powerful 
pump and has a capacity of five gallons. It 
pumps very satisfactorily the asphaltum base 




Application of larvacide or oil by knapsack sprayer: Miraflores 



Attack by Oiling 



167 



fuel oil used in Panama, about 20 Baume, pro- 
vided five per cent, to ten per cent, by volume of 
larvacide is added. 

The advantages of its use are that oil may be 
applied properly on the water surface wherever 
desired from one to twenty feet from the operator. 








Regular Bordeaux. Bordeaux SpcciaL 

Spray nozzles. 

He pumps with one hand and directs the oil-stream 
or spray with the other. The work is less tiring 
than using a watering can, and while traveling over 
rough ground the laborer has both hands free. No 
oil is spilled or wasted by too rapid application. 

It is not necessary to have the spray as fine or 
its particles of liquid as minute as those used in the 
application of insecticide. All that is desired is 
that the oil should spread rapidly upon the water 
and form a thin film. 



168 The Control of Mosquitoes 

Oil may also be applied by using a garden 
watering can; this method is useful where a very 
heavy layer of oil is desired, and where the places 
to be treated are accessible. 

In oiling shallow waters inaccessible from the 
shore, a flat bottomed boat with an oil tank may 
be used. The boat may be propelled by a small 
motor, or by hand, and may have a motor or 
hand-driven pump. A spray nozzle of the type 
shown is very useful, and saves time. 

Two and four-wheel horse carts of special 
design are used on the Canal Zone for applying 
oil. The carts were designed by Mr. H. R. Trask, 
an inspector in the sanitary service of the Canal 
Zone. They consist of iron tanks, holding two 
hundred to five hundred gallons of oil, mounted on 
suitable wagon gear. To the lower sides of the 
tanks are attached three-inch pipes leading to a 
transverse pipe mounted in front, at the feet of the 
driver. This pipe is ten feet long, and the outer- 
most three feet of it is perforated with three rows 
of one-eighth-inch holes set an inch apart. The 
pipe is mounted with a universal joint, and is 
controlled by a leather-operated valve. It is 
raised and lowered by a pedal. In addition, each 
cart is provided with a large valve at the back, for 
withdrawing the oil. 




Field supply tank 




Oil cart for applying oil to roadside ditches 



Attack by Oiling 169 

These carts are very useful where they can be 
driven, and save much labor in transporting and 
applying oil. The illustration shows their con- 
struction. 

They are especially useful in applying heavy 
coatings of oil to roadside ditches, for inhibiting 
vegetation, and preventing collapse and erosion. 

They may also be used for transporting oil from 
the storage tanks to service tanks and drip devices. 

In the jungle covered country of the Canal 
Zone, there are many places where the lightest of 
carts cannot penetrate, and yet are accessible to 
pack animals. These animals carried two fifteen- 
gallon cylinders of oil fastened to the regulation 
pack saddle. These little tanks are provided with 
a two-inch screw stopper for rilling, and a one-inch 
spigot for discharging. The pack mule is especially 
useful when rilling drip barrels situated on streams 
flowing through the jungle, where only trails can 
be used. Trails had to be cut for the mule, but 
the trouble was repaid. One good mule carried 
as much oil as six porters on each trip, and in less 
time. The photograph shows the pack mule 
which has done valiant service in the cause of 
sanitation for about five years. The equipment 
shown is of the simplest type. 

After the oil is sprayed on the water, the 



170 The Control of Mosquitoes 

problem of keeping the oil film in place arises, for 
on water surface of more than a few square feet 
the oil film tends to drift to leeward under the 
impulse of a moderate air current, and leaves much 
water uncovered. 

The tendency to drifting is very difficult to 
overcome. Various devices are in use, all being 
modifications of the "boom" principle used by 
lumbermen to catch log drifts. The simplest 
method is to anchor planks at intervals of five or six 
feet at right angles to the prevailing wind move- 
ment. Where the winds are variable and strong, 
a wooden grille may be employed, with spaces 
inversely proportional to the wind force. 

Stumps, brush, grass, and stones projecting 
through the oil film tend to form oil-free rings 
around themselves by their oscillation, and by the 
breaking of the ripples against these obstructions. 
All such obstructions should be removed from 
areas to be treated with oil. 

The heavier oils in conjunction with algae form 
a tangled heavy mass, and while some of these 
masses sink, many do not, but remain on the 
surface, and produce defects in the film by drifting 
with the surface current. It is well to remove all 
algae from water to be oiled. 

When heavy oil is poured repeatedly and liber- 




Pack mules, for oil transportation in jungle trails 



Attack by Oiling 171 

ally on the common grasses, their growth is in- 
hibited and in time the grasses die. This property 
of the oil is used to advantage on the sides of 
ditches and in shallow depressions where water 
stands during rainy periods, when draining and 
filling is not economically feasible. 

Oil in any form is not an entirely satisfactory 
larvacide for the following reasons : 

Its effectiveness depends on a perfect film. 
Films are unreliable. Perfect films can be ob- 
tained only under exceptional circumstances, and 
even a perfect film frequently develops defects. 

The larvacidal action of oil is slow. In some 
instances several hours must elapse after the oil is 
applied before the larvae of Culex are killed. 
During this time many opportunities may arise 
for the development of defects in the film. The 
light oils are expensive, and the heavier oils do not 
always spread well, unless treated in some manner 
to decrease their specific gravity and viscidity. 

A relatively large amount of oil is needed to 
cover a given water surface, thus increasing the 
cost of handling, especially where the oil has to be 
transported a long distance by hand. 

There is always more or less danger from fire, 
while the oil is in storage. 

The application of oil in the quantity necessary 



172 The Control of Mosquitoes 

to kill mosquito larvae spoils water for use for 
domestic or industrial purposes. 

For certain purposes, however, oil is very useful, 
and in the absence of a more acceptable larvacide, 
the sanitarian must depend largely upon it. 

The defects of oil were soon recognized in 
Panama, and persistent efforts made to find a 
more desirable larvacide. The product named 
" larvacide" in Panama was thus introduced, and 
although short of perfection, is under many condi- 
tions superior to oil. 



CHAPTER XI 

ATTACK ON PROPAGATION AREAS BY LARVACIDES 

T^HE requirements for a good larvacide are: 
* I. That it shall be of high toxic power, so 
that a small quantity may suffice for a large volume 
of water. This requirement is important for its 
economic use in water lying far from roads and 
trails. 

2. That it shall kill rapidly, preferably in less 
than ten minutes, that rain intervening, and con- 
sequent dilution and weakening, may have as little 
effect as possible. 

3. That it be uniform in its toxic power and 
capable of standardization. 

4. That it shall mix freely with brackish and 
alkaline waters. 

5. That it be harmless to man, and domestic 
animals, when in the dilution necessary for larvaci- 
dal action. 

6. That it shall not be susceptible to rapid 
deterioration through age, and exposure to the 

173 



174 The Control of Mosquitoes 

air or light, i.e., it must have good keeping 
quality. 

7. It must be inexpensive. 

A number of commercial products now on the 
market satisfy these conditions to a large extent. 
Many of these have been tried and a few have 
proved equal to some of the requirements. Others 
were frauds. None fulfilled all the requirements 
desired. All commercial products were quoted 
at high prices. The larvacide we finally adopted 
cost one half less than commercial products. 

While working out the problem of a satisfactory 
larvacide, Mr. Jacobs, the chemist of the Board of 
Health laboratory in Panama, suggested the fol- 
lowing formula for a larvacide : 

Resin, 150 to 200 pounds 

Soda, 30 pounds 

Carbolic acid, 150 gallons 

This product is a black liquid resin soap, that 
freely emulsifies with fresh water. In brackish 
or alkaline water emulsion does not take place. 

The active ingredient of the larvacide being 
carbolic acid, to secure uniformity in the larvacidal 
power of the product it is necessary that the active 
constituent of crude carbolic acid, phenol, shall be 
uniform in quantity. It is found that the best 




c 
o 
o 



yd 

°o 
> 



o 

X 



Attack by Larvacides 1 75 

results are obtained with a content of not less than 
fifteen per cent, phenols. In order that the 
finished product may neither float nor sink 
rapidly to the bottom, but diffuse through the 
water uniformly and with fair rapidity, the crude 
carbolic acid should have a specific gravity of 
about 0.97. 

The process of manufacture is as follows: 
One hundred and fifty gallons of the carbolic acid 
is heated in a steel tank fitted with a steam coil. 
When the acid is steaming hot, two hundred 
pounds of powered resin is added and the mixture 
continuously stirred by means of a paddle agitator, 
until complete solution is effected. Thirty pounds 
of caustic soda (sodium hydroxide) is dissolved 
in six gallons of water, and this is added to the 
resin-carbolic acid mixture. The heating and 
stirring is kept up for about five minutes, and then 
a sample of the product is withdrawn, and poured 
into water. If complete and rapid emulsion 
results, the larvacide is ready and is withdrawn 
from the mixing tank into shipping drums. If 
emulsion does not occur, or is incomplete, the 
heating is continued until a sample emulsifies 
satisfactorily. 

Each lot of carbolic acid should be assayed for 
phenol content. Carbolic acid containing less 



176 The Control of Mosquitoes 

than fifteen per cent, of phenols, or of a greater 
specific gravity than 0.97, will not make a satis- 
factory larvacide. 

From time to time, preferably from each lot, a 
specimen of the larvacide should be tested for its 
larvacidal powers. If a I to 5000 emulsion does 
not kill full-grown Anopheles larvae in ten minutes, 
the product is unsatisfactory. 

This larvacide, however, loses some of its effi- 
ciency when exposed, in emulsion, to the action of 
the air, and still more when exposed to contact 
with algae and other organic matter. Under 
the latter conditions its efficiency is lowered con- 
siderably after twenty-four hours' contact, and 
after a few days' exposure its larvacidal power is 
practically extinct. 

The advantages of this phenol-resin soap larva- 
cide are : 

1. High toxicity to mosquito larvae. A 1 to 
5000 emulsion kills full-grown Anopheles larvae in 
from three to ten minutes. 

2. Concentration. Being effective for practi- 
cal use in a 1 to 5000 emulsion, only a relatively 
small quantity of the larvacide need be transported 
to a given body of water. 

3. Uniformity of toxic power. This proauct, 
when carefully made, is uniform in toxicity. 



Attack by Larvacides 1 77 

4. Simplicity of composition. The manu- 
facture of this larvacide requires neither compli- 
cated apparatus nor highly skilled labor. 

5. Low toxicity to higher animals. It is 
practically harmless in ordinary dosage or in 
dilution to cattle, poultry, etc. 

6. Rapidity of toxic action. When used in the 
field, it killed all Anopheles larvae and pupae in 
ten to twenty minutes. 

7. Cheapness of the product. In Panama, the 
cost is about eighteen cents a gallon. 

8. Absence of danger from fire. The con- 
centrated larvacide is inflammable, but not easily 
ignited. In dilution it is not inflammable. 

9. It is useful in the rapid determination of 
the presence of mosquito larvae and kills those 
at rest embedded in the mud. 

10. In addition to its toxicity for mosquito 
larvae the phenol-resin larvacide is also highly 
toxic to protozoa and algae, as well as most of the 
varieties of the common grasses encountered in 
Panama. The algacidal and herbicidal properties 
of this larvacide are of frequent use in mosquito 
eradication. 

The disadvantages of this larvacide are: 

1 . It does not emulsify and is inert in brackish 

water. This is a serious disadvantage because 
12 



178 The Control of Mosquitoes 

many Anopheles breed in brackish water and 
Culex breed in salt-water marshes and pools. 
This defect, however, is shared by all the com- 
mercial larvacides tested on the Isthmus. 

2. The pure larvacide deteriorates upon expo- 
sure to the air and must be kept in drums, barrels, 
and other tightly closed containers. 

3. It rapidly loses its toxicity after mixing 
with water containing algae and other organic 
matter. After twenty-four hours its toxicity is 
so far diminished that it is practically non-toxic 
from the standpoint of field practice. 

The ideal mosquito lavacide should, in addition 
to possessing all the desirable qualities of the 
phenol-resin soap described above, possess none 
of the disadvantages enumerated. We have not 
yet found such a product, either on the market or 
by experimenting with various mixtures. 

The toxic action of the pheno-resin larvacide 
upon mosquito larvae is probably due to the action 
of its phenol content upon the protoplasm of the 
larvae, probably intensified by the fact that the 
phenol is in emulsion. 

We have had practical field experience with 
Pyrocresol. In composition and action this pro- 
duct closely resembled the pheno-resin larvacide 



Attack by Larvacides 1 79 

manufactured in Panama. Its greatest dis- 
advantage was variability of toxicity. Some 
samples were practically inert. The cost of this 
larvacide is considerably higher than the cost of 
the product we used. 



CHAPTER XII 

ATTACK ON PROPAGATION AREAS AND ADULT 
MOSQUITOES BY NATURAL ENEMIES 

PROPAGATION AREAS 

OMALL top-feeding fish which prefer to obtain 

^ their food at or near the water surface are 

of great value in reducing the number of mosquito 

larvae that would otherwise pupate. It was 

frequently observed that they seemed to prefer 

the full-grown larvae and pupae. Many different 

kinds of these fish are found in all parts of the 

Isthmus, in rivers, streams, and drainage ditches 

connected with them. On the arrival of the dry 

season they were often left stranded in small 

puddles and died as these became dry. While 

fish remain in small bodies of water they greatly 

assist in reducing mosquito possibilities, but if the 

water in the pool contains much green algae the 

small fish destroy only a portion of the larvae. 

Where larvae can hide easily, fish catch the fewest. 

1 80 



Natural Enemies 181 

In ditches, streams, ponds, and at the edges of 
lakes and rivers the less the amount of debris, 
grass, algae, or other obstructions, the more useful 
the fish become. It follows that in countries 
where rank vegetation and algae are produced 
rapidly, fish are less reliable as destroyers of 
mosquito larvae than in more northern climates. 

During the first American anti-malaria cam- 
paign at Havana, fish were of greater assistance, 
and reduced the mosquito propagation more than 
in the Canal Zone. Large amounts of finely 
divided debris with bits of twigs and leaves are 
washed down the streams during heavy downpours 
of rain and collect in the lakes and quiet parts of 
rivers. The constant winds collected this material 
and concentrated it. At these places small fish 
were nearly always to be seen, and darted about 
catching the larvae as soon as the sheet of debris 
was stirred up or disturbed. By dipping out and 
stirring a small portion of it in a white enamel 
pail Anopheles larvae in all stages of development 
were seen as well as large pupae; it was evident 
that the fish caught but few of the larvae so hidden. 

When portions of green algae are detached from 
the stream bank, fish invariably follow the float- 
ing mass and work hard for the few larvae they 
catch. They cannot penetrate the mass, nor 



182 The Control of Mosquitoes 

pass through the small openings into which the 
larvae dart. When larvacide is applied at the 
edges of streams, mosquito larvae sometimes escape 
beyond the treated zone and are immediately 
snapped up by fish. When rainstorms remove the 
algae, debris, etc., and break up the hiding-places 
in streams and ditches, the fish are most actively 
employed and have a feast. In quiet waters 
they pick up the larvae that venture far from their 
hiding-places. 

In one instance two solid embankments were 
placed across the Corundu River and extended 
from Diablo Hill to Balboa. Between the embank- 
ments was a large flat area of about five hundred 
acres. During the rainy season much water col- 
lected in it and was followed by a change in the 
character of the vegetation. 

One of the growths was a moss-like weed that 
had not been seen before. It grew in the water to 
within an eighth of an inch or less of the surface 
but did not quite reach it. There was enough 
water above the growth to support Anopheles 
larvae, but not sufficient for the fish to swim in. 
This area was about a mile south of Corozal and 
was not treated until it had produced thousands 
of full-grown larvae. This happened before the 
flight of Isthmian Anopheles was understood as it 



Natural Enemies 183 

is to-day, but the adults that traveled against the 
breeze to Corozal were tracked back to this source. 
Small fish were useless in this case, they could not 
reach the larvae. 

In certain parts of the Bas Obispo River during 
the dry season, shallow water varying in depth 
from an inch to a foot ran over a bottom covered 
with stones and gravel. A thin film of oil was 
generally present, but seemed in no way to interfere 
with the numerous small fish. We knew that 
mosquitoes were still there in spite of oil and fish. 
The film was apparently inadequate to suppress 
many of the larvae, probably owing to free air 
spaces on the downstream side of some of the 
partially exposed stones. 

In the camps affected by this river the malaria 
fever rate had been higher in the dry than in the 
wet season. At all other camps in the Canal Zone 
we had more cases of fever in the wet season. When 
a heavy application of larvacide was given to this 
moving water, numerous Culex and Anopheles 
larvae immediately appeared at the surf ace. Some 
of the fish affected jumped out on to the banks and 
the remainder were killed. Since that time the 
local fever rate during the dry season has not 
exceeded that of the wet season, and year after 
year the adjacent camps have had few mosquitoes 



1 84 The Control of Mosquitoes 

and a very low fever rate. These instances in 
which fish alone have not proved satisfactory are 
not intended to give the impression that fish are 
of small service in combating mosquitoes, but to 
show that on the Isthmus recently developed 
methods of control are more swiftly effective than 
nature's methods of more limited control. Fish 
are most useful under many conditions, but the 
places in the tropics where their control reaches 
perfection are limited. Undoubtedly if all fish 
were removed the number of adult mosquitoes 
including Anopheles might become so great as 
to be unbearable and many places would be 
uninhabitable. 

We believe that the introduction of the proper 
species of top feeding minnows into lakes and 
large ponds would be of decided advantage for 
purposes of mosquito control in countries less 
favorable to mosquito propagation than Panama, 
and that the introduction of fish should be accom- 
plished and the species selected with care, after 
consultation with those competent to give advice 
regarding fish propagation. 

Probably in the near future artificial control of 
mosquito propagation by means of top feeding 
minnows will be used extensively. Many miles of 
drainage ditches on the seacoast meadows of the 



Natural Enemies 185 

State of New Jersey are now being kept entirely- 
free from mosquito larvae by small fish. 

In Isthmian practice we examine places for 
larvae. If fish are able to give us satisfactory 
results so much the better, if not, then fish must 
be temporarily sacrificed to prevent human 
suffering. To profit as much as possible by 
fish control in general mosquito reduction, the 
sanitary authorities introduced the Girardinus 
pcecillodes of Barbadoes into the Isthmus. This 
is a small fish commonly called a "top min- 
now" which feeds at the water surface. The 
female is about an inch and a half long and is a 
rapid breeder. It was bred successfully in tanks. 
The young were liberated in the reservoirs, rivers, 
and ponds and at various parts of Gatun Lake, 
but not in places where fish were unable to control 
the situation and larvacide and oil were used. 

Tadpoles were found in cow hoof -prints when 
water was present, but the Isthmian species did 
not reduce the larvae in the depressions and obser- 
vation failed to prove their value as mosquito 
destroyers. The larvae of dragon flies and water 
beetles were of great value and were found in 
places of a temporary character in which fish 
could not live long and were not found. Probably 
other aquatic insects were of value. 



1 86 The Control of Mosquitoes 

DESTRUCTION OF ADULT ANOPHELES 

Spiders are useful as destroyers of mosquitoes. 
Because mosquitoes prefer to rest on dark sur- 
faces, a black band two feet wide was painted on 
the walls of the barracks at Balboa between three 
and five feet from the floor that they might collect 
where they could easily be reached by the men 
employed to catch mosquitoes. The walls above 
and below this band were white. It was noted that 
after the black band was applied spiders collected 
on it while they were not to be seen on the white 
paint. 

Certain insects are caught and held fast when 
they rest on spider webs, but it is not definitely 
known that Anopheles and other mosquitoes on 
the Isthmus are destroyed in this way. They 
may be caught by spiders while at rest on or near 
the webs. 

Anopheles appear to have no difficulty in leav- 
ing the strand of a spider web which they have 
selected for a resting place. Thousands of spiders 
and millions of ants are to be seen on tall grass 
and weeds growing in shallow water on the 
Isthmus and they probably destroy many newly 
emerged mosquitoes. 

The small lizards of different colored markings, 



Natural Enemies 187 

found in Cuba and on the Isthmus, are constantly- 
catching mosquitoes. They collect insects out 
of doors on the patio walls as well as indoors, 
and after watching them at work, we were satisfied 
that they should be propagated or at least pro- 
tected in every way possible. Near Havana in 
the afternoons they come out on the whitewashed 
walls and never miss a mosquito that dares to 
alight within fifteen feet. They often take four 
moves forward accompanied by rests, before 
making the final rapid dash at the mosquito. 
Sometimes they patrol the walls from about four 
o'clock until dark, and are hard at work again in 
the morning when the mosquitoes come out of the 
rooms and settle on the walls. 

In the Canal Zone they were found in the old 
French barracks. Cunnette camp, near Empire, 
held more than other camps. The buildings are 
on posts about six feet from the ground and one or 
more of the little brown lizards with brownish 
orange colored heads can be seen on the house 
walls at any time. One of these little fellows if 
kept in a screened room would take care of any 
mosquitoes or flies entering when the door was 
temporarily opened, or carried in on clothing. 

Small ants destroy mosquitoes whenever they 
have the opportunity; they even interfered with 



1 88 The Control of Mosquitoes 

our mosquito trap experiments and caged mosqui- 
toes at the experiment station. As soon as they 
find a mosquito trap there is a constant stream of 
them going to and from it and when they have 
disposed of the dead mosquitoes they begin on 
the live ones. One ant catches a mosquito by a 
leg and almost immediately others come to assist. 
In one instance they were seen catching a mosquito 
larva in the cup of water at the base of a banana 
leaf. 

The " night jar" is the most interesting of the 
numerous birds that feed on mosquitoes while in 
flight. At Gatun, these birds invariably appeared 
just before the evening flight began. And in the 
morning they could be heard at the settlement, 
and followed the returning flight from the settle- 
ment back to the breeding place. They dis- 
appeared when the morning return flight stopped. 
After dusk it was too dark to see how late they fed. 

Bats destroy large numbers of mosquitoes near 
houses. Before the houses on the Isthmus were 
screened they passed back and forth through the 
balconies, and the flight range extended only 
a short distance beyond the house. Since the 
balconies were screened they have been more 
numerous between half -past six and seven o'clock, 
which is the time the Anopheles assemble on the 



Natural Enemies 189 

screens. They invariably fly back and forth 
in wind-shaded gullies containing brush, where 
mosquitoes are more numerous than on the 
adjacent higher land. In these sheltered places 
when Culex were swarming about the observers 
and biting them, the bats approached closely, 
while when they were not being bitten by mosqui- 
toes the bats were fully ten feet away. 



CHAPTER XIII 

ATTACK ON PROPAGATION AREAS BY CLEARING 
BODIES OF WATER 

HY removing vegetation, algae, and drift from 
*— " bodies of water, much of the food and most 
of the protection of Anopheles larvae are withdrawn. 
Under normal conditions these larvae prefer to 
remain at the surface of the water where they find 
their food. 

Where vegetation in the water is plentiful, it is 
difficult to use oil effectively, and in order not to 
leave any air holes large quantities must be used. 
Vegetation interferes with the spreading of the oil 
film; it also interrupts the action of the larvacide. 
When rank grasses come up through the water it is 
not easy to see if the oil film is satisfactory or not. 
In moving water, such as ditches and streams, where 
the vegetation is removed the current velocity is in- 
creased, and tends toward washing the larvae away ; 
and by leaving no hiding-place during rainstorms, 

the stream or ditch can be swept clear of larvae. 

190 



The Clearing of Water 191 

Another advantage is that fish and aquatic 
insects that prey on the larvae have no difficulty 
in capturing them and under these conditions 
are extremely valuable in eradicating them. In 
large ponds and at the edges of lakes where larvae 
are frequently found it is often necessary to remove 
all vegetation in the water, and along the shore, 
if it will ultimately reach over into the water. 
Once this is accomplished the fish will keep down 
mosquito propagation until the vegetation again 
becomes rank, or until algae gives the required 
protection. The application of small quantities of 
copper sulphate along the shore or periodical appli- 
cations of larvacide to the small area infested with 
algae will destroy it. Lagoons and many streams 
of slow current contain water surface vegetation, 
such as leaves of lilies, etc., which affords excellent 
protection to the larvae of both Culex and. Anopheles. 
Culex are seen in large patches under these condi- 
tions and may be so close together as to form a 
black mass of thirty or more square feet. This 
takes place even when there are fish. When all 
vegetation is removed, additional fish arrive and 
the larvae soon disappear. To sum up the advan- 
tages to be gained, the clearing of water may in- 
crease the stream velocity, destroy the food supply, 
remove the hiding-places, enable fish to become 



192 The Control of Mosquitoes 

more useful, and produce conditions that cease to 
attract the mosquito. 

Most species of Anopheles will not deposit their 
eggs in bodies of water that would be unfavorable 
to their complete development. They shun locali- 
ties that expose them to natural enemies, lack of 
food, drying up of water, etc. The difficulties in 
clearing bodies of water on the Isthmus are the rap- 
idity with which certain grasses grow up through 
the water and along shore, and the rapid formation 
of algae in shallow water exposed to the sun. 
Where the bottom of a pond is soft some of 
the grasses may be pulled up by the roots by 
means of long-handled potato hooks, and give 
little future trouble. On the Isthmus various 
attempts have been made to prevent the growth 
of vegetation, but no satisfactory economical and 
permanent method has yet been devised. Pre- 
parations containing arsenical compounds were 
tested both in the dry and the wet seasons, in 
ditches, ponds, and depressions on low flat lands 
that became dry. The results were never perma- 
nent, although in some cases vegetation was 
retarded for several months. Certain grasses 
that run flat along the ground and throw out roots 
at each joint grew over ground recently treated 
with arsenical compounds without forming roots, 




Removing vegetation from overgrown streams: 
Machetes are used 




Screened verandas: Ancon 



The Clearing of Water 193 

but as soon as they reached the water in a ditch 
their roots penetrated the soft mud. Experience 
indicated that the results obtained by applications 
of grass and weed destroyers in the dry season 
were better than similar treatment in the wet 
season. In some instances Bermuda grass was 
planted, or encouraged, in order to replace and 
kill other grasses and plants that grow taller and 
are more troublesome and costly to control. 

When it was purposed to use lands near settle- 
ments in the Canal Zone for reservoirs, etc., 
the edges were cleared of vegetation and debris, 
before the water rose, and the grass was cut very 
short just above and below the proposed water 
surface elevations. All dead vegetable matter on 
the ground to be flooded that might float on the 
water surface was collected and burned. 

As a result we had bodies of water that were 
relatively free from floating timber, sticks, leaves, 
debris, etc., and with edges in a condition that 
allowed oil or larvacide to be rapidly and economi- 
cally applied whenever and wherever necessary. 
Near small or temporary camps where conditions 
did not warrant much expenditure of funds, the 
trees in lagoons and flooded areas were not removed. 
Under the above conditions it was found best 

to remove brush, grass, and floating sticks and 
13 



194 The Control of Mosquitoes 

debris, which afford better protection to mosquito 
larvae than is given by standing trees. When 
trees are not standing close together, unless their 
branches reach the water surface, collections of 
debris are not apt to gather and remain near them. 
In the absence of an oil film small fish devour 
most of the larvae close to the tree trunk. After 
the tree decays and falls, its twigs and branches 
may tend to collect floating debris and afford 
protection to larvae. In the tropics vines and 
plants may grow on floating logs and become the 
nucleus of floating islands. 



CHAPTER XIV 

ATTACK ON PROPAGATION AREAS BY REMOVAL OF 

JUNGLE 

ft /I ANY square miles of jungle in the Canal 
* Zone have been removed since the American 

occupation, including all camp and town sites 
with their surrounding cleared areas, and charged 
against sanitation. In 1904 some of the houses 
could not be reached without cutting a way through 
the intervening jungle. This first clearing was 
made by using the "machete," and the native 
laborer is at his best in using this instrument. 
Until this clearing was made, it was impossible 
to locate the breeding places near settlements, or 
to follow up streams or small natural watercourses. 
The seepage areas, pools, and water-holding depres- 
sions were frequently covered and hidden. 

Clearing uncovers many propagation areas, 
and when the sun and wind act on the cleared 
spaces, evaporation is greatly increased, and 
numerous small ones become dry before a brood of 

195 



196 The Control of Mosquitoes 

mosquitoes matures. It also facilitates inspection 
and enables the location and extent of the seepage 
outcrops to be determined. It shortens the effec- 
tive length of the wet season so far as mosquito 
production is concerned, and makes it possible to 
locate all new small temporary production areas 
that may exist during excessively wet periods. 
We found it advisable to clear the ground before 
locating ditches, to ensure their correct placing. 
The jungle was so thick that on relatively flat 
lands it was impossible to determine the position 
of the low places by inspection, for when wander- 
ing around in the brush it is easy to lose all sense 
of direction. Adult Anopheles and other mosqui- 
toes rest in the shade, and the removal of the 
jungle reduces the number that enter dwellings. 
Clearing made it impossible for the negroes to 
throw containers into the tall grass or brush near 
their houses without detection. They were accus- 
tomed to throw them away and would carry 
unserviceable containers a long distance to dispose 
of them rather than put them in the neprby 
garbage cans! We cut pathways along the edges 
of streams and ditches, cleared the edges of ponds, 
and removed grass from puddles and wet lands to 
facilitate the application of oil and larvacide. 
Much of the clearing in lagoons had to be done 



Removal of Jungle 197 

from boats. In wet periods certain grasses and 
plants grew an inch or more per day, and the work 
had to be done repeatedly over the same territory. 

Toward the end of the dry season, spaces were 
cleared by fire, whenever they could be b:-rned 
over without danger to property because of the 
trade winds that assist in spreading flames. Near 
all permanent settlements where the topography 
permitted, the ground was prepared for using 
mowers, and on some steep hillsides heavy spikes 
were used on the wheels to prevent the machines 
from sliding downhill. This was especially neces- 
sary where the hillside terminated at the abrupt 
canal banks. At times, when the tall grass needed 
cutting, the ground was so soft that the use of 
horses meant the creation of many new breeding 
places by hoof -prints, etc. If the grass remained 
uncut, evaporation was retarded and mud breed- 
ing aggravated conditions. 

The day's work had to be arranged according 
to weather conditions. 



CHAPTER XV 

SCREENING AND PRACTICAL DESTRUCTION OF ADULT 
ANOPHELES IN HOUSES 

QINCE Sambon and Low with their two com- 
^ panions lived for three months in their 
screened hut in Ostia, Roman Campagna, where 
malaria is usually prevalent, without contracting 
it, attention has been directed to the possibility 
of securing protection from mosquitoes by pro- 
tecting the dwellings with mosquito-proof material 
and a variety of fabrics have been used in various 
places and many details of technique have been 
elaborated. After many experiments, both in the 
laboratory and in practice, the methods of mos- 
quito-proofing described are now used in the 
Canal Zone, where screening of dwellings has been 
carried out on a scale never attempted elsewhere. 
Because of the atmospheric humidity and the 
salt laden air it was found that only the best 
copper gauze will resist corrosion and subsequent 

deterioration. The copper gauze used in the 

198 



Screening and Destruction 199 

Canal Zone must have not less than ninety per 
cent, of pure copper, and not more than one half 
of one per cent, of iron. The cost of this screening 
is approximately fifty cents per square yard for the 
18 mesh, No. 31, B. W. G. gauze, i.e., gauze having 
eighteen strands of wire of one one hundredth 
of an inch diameter in each linear inch, which 
is the number of strands necessary to reduce the 
apertures to a size that will not permit the passage 
of A'edes calopus and the smaller specimens of 
Anopheles and Culex, and yet retain reasonable 
strength of material and open space area. 

Verandas are usually screened as shown on the 
photograph. In the tropics the veranda is practi- 
cally the living room; people usually spend their 
evenings in it, and it must be screened. Aside 
from the fact that screened verandas contribute 
very largely to the comfort and probably to the 
health of the occupants of the dwellings, screening 
on verandas is easier and cheaper to maintain than 
the screening of many doors and windows that 
would otherwise have to be screened. And 
because of their larger air and light admitting 
area, screened verandas do not exclude quite as 
much air and light as screened doors and windows. 

A decided advantage is gained by having but 
one door through which mosquitoes may enter. 



200 The Control of Mosquitoes 

Unless near a wall mosquitoes do not congregate 
about the door of a screened veranda as they 
do about a screened door in a solid wall. They are 
too busy examining all the screened surface to 
concentrate at its entry. 

If there is a prevailing wind direction during 
the mosquito breeding season it is advisable to 
have the balcony door on the windward side of 
the house. 

Where windows have to be screened, the sashes, 
shutters, and frames are so arranged that a per- 
manently fixed screened frame can be fastened 
in place. Sliding screen frames are very unsatis- 
factory in practice; they warp and refuse to shut 
tightly, they cost more to install and maintain, 
and are often left open. 

A light solid door, well designed and made, 
and rapidly self closing is preferable for a mosquito- 
proof house. In damp countries such doors 
should be made of close-pored lumber, well dried 
and carefully filled and varnished, or painted, 
and designed to reduce to the minimum the 
tendency toward sagging, warping, and swelling. 
The doors should be provided with efficient self- 
closing devices, and they should open outward to 
frighten away any mosquitoes resting on or near 
the door or hovering in the vicinity. Occa- 




r o #* t 



PL 



ylflfl 




| AFTER 
'I APPLIED 

! £ 






sit 
1 

ii 




A good device to prevent the sagging of screened doors 



Screening and Destruction 201 

sionally, when mosquitoes are very numerous on 
hospital buildings, especially yellow fever wards, 
it is desirable to double-guard the entrance by 
providing a screened vestibule. Such a vestibule 
should be at least six feet wide from door to door, 
and should be arranged so that one door must be 
closed before the other can be opened. A number 
of devices will readily suggest themselves. One 
that has been used with considerable success is 
a pulley and rope arrangement. 

If screened doors are to be used, the frame should 
be made of light material that will resist warping 
and swelling, and should be provided with a brace 
to prevent sagging. A good contrivance for this 
purpose is two rods connected by a turnbuckle. 
One free end is fastened at the upper corner on the 
hinge side of the door, and the other free end to 
the corner diagonally opposite, as shown on the 
diagram opposite. Tendency to sagging is cor- 
rected by twisting the turnbuckle. 

The screen panels should be protected from 
injury by hands and feet by fastening over the 
gauze on the outside of it, so as not to interfere 
with any mosquito catching that may be required, 
one quarter inch or three eighths inch galvanized 
wire netting made of wire sufficiently thick to 
resist denting by a push of the hand or foot against 



202 The Control of Mosquitoes 

the panel. Screen panels should not be more than 
three feet wide and eight feet long. Wider or 
longer panels resist wear less satisfactorily. 

The screening should be fastened with copper 
tacks to prevent galvanic action, and the edges 
overlaid with wooden strips three-eighths of an 
inch by one inch, and fastened with galvanized 
wire nails. The tacks should be placed at least 
one half inch from the edge of the screening. 
The screening should be drawn as tight as possible, 
without the aid of special stretching devices; i.e., 
it should be stretched tightly enough to prevent 
denting and consequent breaking in cleaning, but 
not so tightly as to put immoderate strain upon 
the strands bearing against the tacks. 

It was found advantageous to protect in a 
similar manner the lower panels of verandas, the 
lower parts of the panels above hand rails, panels 
immediately adjacent to doors, and other panels 
subjected to hard usage by the inhabitants. 
Strips of wood have not proven satisfactory in the 
protection of screening. They have the inherent 
defect of interfering seriously with the success of 
mosquito destruction within the houses. 

When screening is kept clean, by frequent 
removal of the dust and the products of corrosion, 
the amount of light and air excluded by the eigh- 



Screening and Destruction 203 

teen-mesh gauze used on the Canal Zone is negli- 
gible. The best proof that screening does not 
materially interfere with the comforts of the house 
occupants is the fact that not a single complaint 
has ever been heard on that score from the people 
on the Zone. 

It was occasionally necessary to use tents and 
railway cars for quarters. The method of making 
tents mosquito-proof was as follows: A matched 
lumber floor is laid, and on this are built up the 
sides of a framework of two by fours, with the 
necessary doors. These frames are screened. The 
ridge pole is formed by two vertical two by fours, 
and one horizontal member, properly braced. 
Brackets of the right length and height are fas- 
tened to the wall frames at intervals. The tent is 
fastened to these brackets by pulling it tightly over 
the upper horizontal members of the wall frames, 
and fastening it to the members by clamping 
strips of wood to form mosquito-proof joints. 
Over the tent roof a fly is drawn, and its edges 
fastened near the ends of the brackets to leave a 
space of at least fifteen inches between the tent 
and the fly edges. 

In the railroad construction camps, screened 
cars are used. The cars are screened in the same 
manner as the dwellings. The illustration shows 



204 The Control of Mosquitoes ] 

some of these cars. A camp consisting of screened 
cars, and a tent hospital screened in the manner 
outlined above, have been in use for about four 
years. Although Anopheles were very numerous, 
as shown by the daily catches in the cars, and 
although very little oiling, etc., was done in this 
locality, the screening, plus daily catch of mos- 
quitoes in the cars, kept the malaria incidence 
to almost the average incidence of the Canal 
Zone. 

The crucial point about screening is the thor- 
oughness with which the work is done, and the 
constant vigilance and care that must be exercised 
in speedily detecting and remedying defects. 
Mosquitoes, and particularly Anopheles, will 
readily find a very small aperture in their endeavor 
to enter a house to find blood, but once within a 
house, the mosquito very seldom, if ever, finds 
its way out again unless doors or windows are 
open. A screened house with rents in the screen- 
ing, cracks in the floor, openings between the plate 
and roof, or any of the many imperfections of 
mosquito-proofing, is a veritable trap, and from 
the point of view of the protection of its inhabitants 
from mosquitoes, more dangerous than an un- 
screened house. 

A perfectly screened house may yet offer in- 




Types of screened houses : Colon Hospital grounds 



Screening and Destruction 205 

numerable avenues for the entry of mosquitoes. 
To enumerate a few of these: cracks and knot 
holes in the floor; ill-fitting doors; spaces between 
a corrugated iron roof and the plate left uncalked; 
cracks in the siding of an unsealed frame building; 
open spaces around plumbing, stove pipe, etc. 
In the Canal Zone, with the extreme variation 
in humidity between the dry and wet seasons, 
defects develop constantly in the woodwork of the 
light frame constructions employed. The screen- 
ing is also exposed to rather severe strain. To 
maintain efficiently the mosquito-proofing of 
the dwellings, a weekly inspection was made of all 
the screened houses, and the needed repairs noted, 
and made at once. Since 1908 the repairing of 
screening has been delegated to the Quarter- 
master's Department for administrative reasons. 
From the standpoint of sanitation, it is wiser to 
maintain a screen-repairing force under the 
immediate control of the sanitary authorities, to 
insure this important work being done by a force 
specially trained to detect defects in mosquito- 
proofing, and to render dwellings mosquito-proof 
unhampered by the interference of other duties. 
After experience with both systems, the writers 
earnestly recommend that all questions of mos- 
quito-proofing should be entrusted to the sanitary 



206 The Control of Mosquitoes 

authorities, who are more competent to judge 
the importance of the defects deemed unworthy 
of attention by the average layman, builder, and 
architect. 

In a malarious locality the screening of dwellings 
is a necessity. With a view to determining as 
nearly as possible the difference in malaria infec- 
tion between the inhabitants of screened and 
unscreened dwellings at Gatun, a study was made 
by Dr. Orenstein. The conclusions reached were 
that screened dwellings reduce the malaria inci- 
dence by at least one third. 

It is almost certain that the protection afforded 
is greater than this study showed, for the reason 
that while the people residing in the screened 
quarters of Gatun were obliged to consult a govern- 
ment physician when incapacitated for duty by 
illness, the residents of the unscreened section 
were not required to adhere to this rule, and con- 
sequently there is no record of a probably large 
number of cases from these houses. 

INFORMATION CONCERNING METALLIC MOSQUITO 
SCREENING 

1 6 mesh copper alloy gauze will permit the 
passage of A'edes calopus only under stress of 
circumstances. 




Types of screened houses : Culebra 




Screened cars in railroad construction camps 



Screening and Destruction 207 

17 mesh and 18 mesh will exclude this species. 
16 mesh will exclude Anopheles. 

16 mesh — Area of aperture 0.00235 square inch. 

Wire No. 28 B. W. G. — Diameter 0.014 

inch. 
Weight per square foot 0.2224 lb. 
It is twice as strong as 18 mesh. 
60.16% of open space. 
95% increase in area over No. 31 B. W. G. 

17 mesh — Area of aperture 0.00219 square inch. 

Wire No. 30 B. W. G. — Diameter 0.012 

inch. 
Weight per square foot 0.17339 lb. 
It is 50% stronger than 18 mesh. 
63% of open space. 
43% increase in area over No. 31 B. W. G. 

18 mesh — Area of aperture 0.00208 square inch. 

Wire No. 31 B. W. G. — Diameter 0.01 

inch. 
Weight per square foot 0.12835 lb. 
67.39% oi open space. 

All copper alloy used in screening should contain 
not less than ninety per cent, copper and less than 
one half of one per cent, of iron. 

DESTRUCTION OF ADULT ANOPHELES 

In addition to the screening, a further decrease in 
the possibility of infected mosquitoes transmitting 
malaria can be accomplished by daily destroying 



208 The Control of Mosquitoes 

the Anopheles found in the dwellings. This has 
been systematically carried out in all the barracks 
in the Canal Zone, and is considered a very valu- 
able measure when painstaking men are employed. 
Systematic mosquito catching in dwellings as a 
prophylactic measure against malaria originated in 
the Canal Zone. Briefly, it was the adaptation to 
sanitary purposes of the method employed by the 
entomologist in securing specimens. It was first 
tried in 1908 by W. R. Proctor, sanitary inspector, 
in a temporary camp known as Cocoli. This 
camp was in close proximity to extensive Anopheles 
breeding areas. Because of the camp's temporary 
character, more thorough methods of eradication 
were not used. Malaria soon developed among 
the laborers in the camp, and the incidence of this 
disease became very high. 

Although there was much doubt concerning the 
efficacy of mosquito catching as a means of reduc- 
ing the malaria incidence, it was tried as other 
measures could not be applied. To the surprise 
of all, the systematic destruction in the camp 
speedily reduced the malaria incidence. The 
catching was done at sunrise and sunset, by a 
negro laborer. 

Mosquito catching in dwellings was then adopted 
as one of the regular prophylactic measures. 



Screening and Destruction 209 

During 1909 a number of camps were located 
along the new line of the Panama Railroad, 
officially known as the Panama Railroad Reloca- 
tion. This is to be the permanent railroad after 
the Canal is completed. Four of these camps, 



Months. 



January. . . 
February . 
March .... 

April 

May , 

June , 

July 

August 

September 
October. . . 
November 
December. 



Average permonth 



1909. 



Con- 
struc- 
tion 
Camps. 



•94% 



.94% 



Entire 
Zone. 



1.50% 



1.50% 



1910. 



Con- 
struc- 
tion 
Camps. 



1.55% 

• 67% 

1.44% 

2.50% 

2.30% 

2.41% 

3.29% 

1.34% 

.96% 

2.59% 

.50% 

.77% 



1.53% 



Entire 
Zone. 



.96% 
•71% 
1.04% 
• 81% 
1.16% 
2.42% 
3.39% 
2.81% 
1.76% 
1.25% 
1.16% 
1.16% 



1.55% 



1911. 



Con- 
struc- 
tion 
Camps. 



• 67% 

•42% 

.28% 

..56% 

1.94% 

5 ..06% 

2.84% 

1.36% 

2.64% 

2.58% 

2.58% 

1.21% 



Entire 
Zone. 



.72% 

.77% 

.85% 

.68% 

1.91% 

3.59% 

4.14% 

1.82% 

1.40% 

1.00% 

• 82% 

.'76% 



1.54% 



Remarks. 



Dry Season. 
Dry Season. 
Dry Season. 
Dry Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 
Rainy Season. 



Table of malaria incidence at construction camp. 

with an aggregate population of about 1200, were 

located along twelve miles of the road, at intervals 

of three to four miles. 

It would have been costly to attempt drainage 

and oiling operations of sufficient magnitude to 

protect all these camps from malaria, and it was 

decided to house the employees in screened cars, 

and to carry out daily mosquito catching in all of 
14 



210 The Control of Mosquitoes 

them. The number of Anopheles caught in the 
cars, which were surrounded by mosquito breed- 
ing places, reached 1800 a week. The malaria 
incidence in these camps was but slightly above 
the incidence for the Canal Zone shown in the 
table. It will be observed that in 19 10 the 
malaria incidence was two one hundredths of one 
per cent, less for the camps, and in 191 1, three 
tenths of one per cent, more, as gauged by admis- 
sions to the hospital. It must be remembered, 
however, that the percentages for the whole Zone 
are based on the final diagnoses made by the exam- 
ining physician. Experience has shown that the 
examining physicians sometimes give a provisional 
diagnosis of malaria in a somewhat larger number 
of cases than the final diagnosis sustains. 

Another instance of the application of this 
prophylactic measure under more favorable condi- 
tions occurred near Corazal. In this case the 
camps were remote from native habitations. In 
June, 1908, several hundred United States marines 
were quartered for two months on Diablo Hill. 
During that period the malaria incidence among 
them averaged fourteen per cent, a week. No 
mosquito catching was done. Some cars in which 
railroad laborers lived were located at the foot 
of the same hill. From the early part of May to 



Screening and Destruction 211 

the end of November, in the rainy season, when 
malaria incidence is high on the Isthmus, only 
four cases of malaria occurred among the forty 
laborers occupying these cars — a weekly incidence 
of three tenths of one per cent. The difference 
was due to having a man devote half an hour a day 
to the destruction of the Anopheles found in these 
cars. The work cost five cents a day. 

The technic of hand catching is as follows: A 
glass tube about four and one half inches long 
and one inch in diameter, of the variety used for 
packing small camel hair brushes, is used. An 
inch layer of small rubber bands is packed into the 
bottom of the tube. They are held in place by a 
plug of absorbent cotton, which in turn is covered 
by a disk of blotting paper to facilitate the removal 
of mosquitoes from the tube, by preventing their 
entanglement in the cotton. A few cubic centi- 
meters of chloroform are poured into the tube, 
which is then covered, and the chloroform allowed 
to become absorbed by the rubber bands. A tube 
thus prepared will be lethal to mosquitoes for 
several days. The chloroform tube has the ad- 
vantage of being safer than the cyanide tube in 
the hands of a more or less careless laborer. To 
catch a mosquito with the tube, the cork is re- 
moved, and the mouth of the tube quickly placed 



212 The Control of Mosquitoes 

over the mosquito while it is at rest on some 
object. In a few moments the mosquito drops to 
the bottom of the tube. 

Equipped with one of these tubes, a "slapper" 
made of a six-inch square of wire gauze fastened 




Slapper, chloroform tube, acetylene lamp, and pill box; used 
in catching Anopheles in houses. 

to a two-foot stick, and, if necessary, a bright 
search-lamp or portable electric light and cord, 
an ordinary laborer will soon learn to catch a 
surprising number of mosquitoes. That mosquito 
catching in dwellings may be facilitated, prefer- 
ably white or light colored walls should be insisted 
upon. Anopheles rest during the day in the 



Screening and Destruction 213 

darkest nooks in the room; in remote dark corners, 
behind various objects on the wall, and under 
window ledges, etc. Careful search is required 
to find them and on a dark colored wall they are 
almost invisible. 

In the early morning hours soon after daybreak, 
and in the twilight hour of the evening, Anopheles 
usually collect on the screening of verandas, 
doors, and windows, and are more easily caught 
than when indoors. The chloroform tube does 
not work very well on screening and the "slapper" 
is employed. 

The cost of mosquito catching in dwellings is 
very slight. We employed common laborers at 
ten cents an hour. One man can cover a score 
of barracks in two or three hours. If the houses 
are in a group, an experienced mosquito catcher 
will examine as many as twenty in three hours. 
Of course, the number of houses covered depends 
on their size, the number and interior arrangements 
of the rooms, the number of mosquitoes found, 
and the distance from one house to another. 
The statement made above regarding the number 
of houses a man can examine, refers to the standard 
barrack of the Canal Zone, a one-room, one-story 
building about forty by sixty feet. 

In the early part of 191 1 hand catching was 



2i4 The Control of Mosquitoes 





Wire Screen High Ridge 
Frame of White Pine 



"3k" .^t_ 

l ar n i r in i 

I - i ' o" n 
r n — 8-r-H | 
pf 9H — ■ *j 



Wire Screen Low 

Ridge 
Frame of White 

Pine 



..i— 



Mosquito trap, with details of construction. 



Screening and Destruction 215 



supplemented by mosquito traps. The evolution 



^Ek 




H — :,Hoi — »■ 



n. 




o 
m 

■*-> 
u 






? o 



S 



of the mosquito trap into the model used at present 
has been gradual. The first trap constructed, 



216 The Control of Mosquitoes 

while ingenious, failed in its purpose — mosquitoes 
simply would not enter it. Gradually by develop- 
ing the original ideas and plans of the senior author 
and by constant experimenting under his immedi- 
ate direction, Messrs. Bath and Proctor, sanitary 
inspectors in the Canal Zone service, evolved 
the Anopheles trap now in use. 

This trap is essentially a labyrinth built of wire 
gauze on a wooden framework. The illustrations 
on pages 214 clearly show its construction, and 
method of application to a screened window. As 
a mosquito catcher, the trap is of great service 
when properly used. It was found that in order 
to catch Anopheles the traps must be attached 
to the lee side of buildings, and that usually more 
Culex are caught if the trap is fastened on the 
windward side. The reason for this is yet to be 
determined, but the phenomenon is a fact, and 
should always be remembered when installing the 
traps. The possibility of some species of Anopheles 
being attracted by scent was considered. When 
two adjacent buildings were supplied with Anophe- 
les traps, one inhabited and the other vacant, no 
Anopheles entered the traps attached to the vacant 
building. 

It is found that more mosquitoes are caught 
when they are attempting to enter a building. 




Interior of laborers' barracks, where Anopheles were caught daily 



Screening and Destruction 217 

Therefore traps are installed with their openings 
turned outwards and are not used for collecting 
the Anopheles which have already gained access 
to the building. 

Traps are of little use on unscreened houses and 
are never used on them. 

The number of mosquitoes caught in these 
traps has been surprisingly large and it is not 
uncommon to catch several hundred per night in 
one trap. 

In order to determine whether any mosquitoes 
escape, a trap in which a number of mosquitoes 
were confined was fastened to an empty trap. 
None passed from one trap to the other. If they 
could have found the openings in the trap in which 
they were confined they would have collected in 
the other trap. 

Mosquito traps, built after the model used on 
the Canal Zone, are of distinct value as a prophy- 
lactic measure in anti-malaria campaigns, as an 
auxiliary to screening, and the destruction of mos- 
quitoes by hand. 

These mosquito traps cost about $1.25 each 
when made by hand by the dozen. 



CHAPTER XVI 

THE RESULTS ACCOMPLISHED BY THE ANTI-MALARIA 

CAMPAIGN 

T^HE methods of malaria control applied and 
* developed on the Isthmus were put to a 
severe test and gave successful results. The 
topography, meteorological conditions, and con- 
stant changes due to the construction work, to- 
gether with the character and constant moving of 
the population and their dwellings, and social 
conditions, were peculiarly unfavorable to the 
control work undertaken. The natives and em- 
ployees, infected or well, were at liberty to live 
where and how they chose. We had no control 
over their movements or methods of living. 

The area covered by anti-malarial operations 
was about fifty square miles, with a shifting 
population of many nationalities. It is now evi- 
dent that even under such adverse conditions, 
malaria in the tropics may be kept down to a 
minimum rate without prohibitive cost. 

218 



Results 219 

Much valuable experience has been gained, 
that will aid future anti-malarial campaigns, and 
these newly devised methods of procedure and 
the important discoveries made as the work 
progressed will now make it possible for many 
sections of the tropics to develop their agricultural 
and natural resources. 

Until now Aedes calopus and a few species of 
Anopheles have prevented the Caucasian race 
from settling and developing the tropics. In some 
of the richest parts of the United States more 
than fifty per cent, of the agricultural population 
is infected with malaria. In some parts of the 
tropics the malaria rate exceeds seventy-five per 
cent, of the rural population, and the transmission 
of infection often continues throughout the year. 
Under such conditions can progress or social 
development be expected? 

In South America there are parts of the sea- 
coast, and even cities, to which laborers from the 
hill-country cannot be induced to go. They 
refuse a high rate of wage, and their reasons 
and judgment are sound. In recent railroad 
construction in Brazil, European laborers 
would not remain in the company's employ 
although paid an exceedingly high rate of wage. 
Where eighty per cent, of the laboring force is 



220 The Control of Mosquitoes 

sick at the same time their actual earnings are 
small. 

The rich lands in malarial sections of the tropics 
cannot be economically developed without syste- 
matic malaria control. It is no longer a question 
of whether a corporation can afford to pay for 
the necessary anti-malaria measures; it is now 
admitted to be foolish to attempt development 
without reasonable sanitary precautions. 

The preventive measures taken in the Canal 
Zone cost less than one cent a day for each 
person. 

During the reconstruction of the Panama 
Railroad, in many camps we housed laboring 
forces in outfit-cars surrounded by extensive 
swamps, where drainage or economic control of 
mosquito life was impossible. By screening the 
cars, and destroying Anopheles in them once a day, 
the infection of laborers was prevented. Live 
mosquitoes caught daily in the cars were examined 
for parasites, but no infected specimen could be 
found. These preventive measures had not been 
attempted before, but can be applied again, and 
the efficiency of our troops on the Isthmus, and 
elsewhere, may be kept up to the standard. 

Large forces of men employed in commercial 
enterprises may now be kept in good health where 



Results 



221 



sickness formerly made their day's work uncertain. 



MALARIA CHART 
for 1911, 1912 and 1913 

Showing the number of malaria cases each 
month among employees, expressed as a per- 
centage oTfhe entire working force. 

A 



1 




tktv %fc*>/-f* % 



^ u M U u u $ 



The item of high labor cost, because of malaria, 
has been a controlling factor in preventing progress 
in the South. 



222 The Control of Mosquitoes 

It has been ascertained that marked differences 
exist in the habits and life history of different 
Anopheles i and between Anopheles and other 
mosquitoes. We learned how to observe their 
flight, and that the malaria-carrying species can 
be stained, and by this means it can be determined 
how far and in what direction they travel; and 
by intercepting them in the path of their flight, 
they are made to register its general direction. 
It was established that some species of Anopheles 
travel farther than others. 

It was observed that while Culex, and possibly 
other mosquitoes, enter a residence on the wind- 
ward side, Isthmian Anopheles seldom do this. 
The importance of placing screened entrances 
and verandas on the windward side is now under- 
stood, but had not previously been considered. 
A method of making Anopheles trap and destroy 
themselves has been perfected; and it has been 
determined that some species avoid bright artificial 
light. 

New methods of collecting specimens have been 
devised. 

The migration of one species across the Isthmus 
was closely observed. Previously it was thought 
that malaria increased in proportion to the number 
of Anopheles in a malaria-infested community, 



Results 223 

but Isthmian observations show several instances 
to the contrary. Where Anopheles tarsimaculata 
and Anopheles albimanus traveled long distances 
from the breeding to the feeding grounds their 
number at the settlements greatly increased, but 
the malaria rate did not rise. It is of great 
importance to know if these facts hold true in 
regard to other malaria-conveying species, as such 
facts determine the right areas for malaria control 
operations. 

Due to factors not fully ascertained the same 
species do not always fly long distances, or even 
a quarter of a mile, to reach a house or village. 
Since learning how to observe and follow a flight 
we can now decide correctly which location to 
drain or treat for the protection of a town or 
settlement, and leave out the unessential. 

The varying distance of mosquito flights of 
which so much, assumed and untrue, has been said 
and written, no longer appears impossible to 
solve. At present the important point to decide 
is the length of flight of different species of Anoph- 
eles in so far as it affects malaria transmission, 
and this may differ from the flight length probably 
essential for the propagation of the species. 

The decidedly brackish marshes and the edges 
of shallow tidal flats, which were once the chief 



224 The Control of Mosquitoes 

sources of Anopheles at Gatun, Chris tobal, and 
Colon, presented conditions that may not be 
limited to the tropics, and afford precedents for 
future anti-malarial work near seacoasts farther 
north. 

Although the Anopheles is usually considered a 
night-biting mosquito, Isthmian observation has 
proved that some species bite people in the day- 
time, both in houses and in forest shade ; and when 
very numerous these insects appear less afraid of 
capture or exposure to natural light. In one 
instance Anopheles tarsimaculata and Anopheles 
albimanus bit freely all day in the sunlight, but 
this was the sole exception noted during more than 
twelve years of observation. 

Other new facts of importance ascertained and 
improvements devised relating to control measures 
that resulted in reducing the cost and increasing 
the efficiency of anti-malaria work were : 

Concentrated larvacide, effective when and 
where oiling is useless, is now made and trans- 
ported economically. 

Practical tests were made to discover the cause 
of the decay of copper alloy screening. It was 
found that monel metal mosquito wire, sixteen or 
eighteen mesh, remains intact after the best grade 
of copper bronze wire has decayed. 



Results 225 

Devices for making wire screening continuously 
effective, together with systematic inspection 
and repair. 

The complete eradication of mosquito- producing 
conditions in hillside ditches and the elimination 
of maintenance costs by the introduction of a 
thin reinforced concrete lining of special design. 

The elimination of seepage water breeding areas 
by the use of special methods designed to suit 
local conditions, where standard methods of sub- 
surface drainage were valueless. 

The use of automatic oil drips to control mos- 
quito breeding in running water in streams and 
ditches, and that of oil-soaked waste for small 
see page outcrops. 

In describing the use of oil on the Isthmus Dr. 
Malcom Watson, who has had extensive experi- 
ence in measures for malaria eradication, and 
directed the successful control of malaria in the 
Federated Malay States, after inspecting the 
methods used at Panama, reported to the Royal 
Colonial Institute as follows : 

As the greatest sanitary achievement the world has 
seen, it has a lesson for us. I went there because 
I wanted to study the details of their methods, in 
particular how much of their excellent results was 
due to drainage, and how much to screening, oiling, 
is 



226 The Control of Mosquitoes 

and quinine. From my visit I concluded the results 
were mainly from oiling, which was done for practi- 
cally half a mile on each side of the canal, or at least 
the inhabited portions of the Zone. The great 
majority of the population do not live in screened 
houses and very few take quinine. Drainage is 
constantly interfered with, and there is no agriculture. 
Colonel Gorgas had therefore everything against him 
except the determination to win and money to back 
him. Depending on oiling the organization has to 
be, and is, perfect, for failure for a single week would 
allow mosquitoes to develop. Their position is as if 
they had a wild beast by the throat, but were not 
allowed to kill it ; yet if for a moment their grip were 
to be released, the beast would be on them. No 
greater sanitary work has been done: I doubt if we 
will see as great again. It is perfect work, and its 
organization is the only kind that would have suc- 
ceeded under the circumstances. Some of the methods 
I saw are already being put into action in the Fed- 
erated Malay States on my advice. 

The health officials had no control over the 
selection of camp sites, yet were expected to main- 
tain the standard of good health of the laborers. 
In some cases the camps were placed near prolific 
Anopheles production areas, and no extra funds 
provided for their treatment. Similarly difficult 
problems and conditions were brought about by 
unnecessary obstructing of natural watercourses 
and flooding hundreds of acres of jungle near 









































































































































































































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MALARIA IN THE CANAL ZONE; ISTHMUS OF PANAMA 

Malaria cases among the employees of the Isthmian Canal Commission 

[FROM NOV. 1905 TO 1913] 

This Chart shows the number of Malaria oases, admitted to hospital each Month; 
expressed as a percentage of the entire working force 










































































































































































































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Malaria in the Canal Zone: Isthmus of Panama 



Results 227 

populated districts. Had the necessary topo- 
graphical changes been considered or foreseen, the 
advantage of selecting other camp sites would have 
been obvious. 

The proximity of proposed camp sites to exten- 
sive Anopheles producing areas, or native villages 
in which many cases of malaria exist, merits careful 
consideration. 

The old idea of locating a house on a small hill 
to escape "malaria miasma " is of little importance. 
The slight advantage gained is only that of in- 
creased air motion causing temporary protection 
from mosquitoes. 

The selection of poor locations for camps, and 
the creation of new and extensive Anopheles pro- 
duction due to topographical changes, and other 
causes, produced fluctuations in the malaria sick 
rate, many of which might have been avoided. 

By studying each problem separately and 
devising methods to solve it, and concentrating 
effort on the most important points of attack in 
order to obtain the largest net returns for each 
dollar expended, we were able to reduce, from year 
to year, the malaria sick rate of the force employed. 

The malaria charts show the results accom- 
plished. 






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Hospital Cases of Malaria among Employees -1906-1913 
Compiled by adding monthly percentages of force sick with malaria 



PART II 

The Yellow Fever Campaign 



229 



CHAPTER I 

THE CAMPAIGN IN HAVANA 

THE measures adopted to eradicate yellow 
fever from the Isthmus were based upon 
the knowledge gained from the work done by 
Colonel Gorgas and his associates in the eradi- 
cation of yellow fever in Havana, Cuba. Havana 
was the first place in which anti-yellow fever 
measures were carried out with success, working 
along lines suggested by the theory of Carlos Fin- 
lay, and observations of H. R. Carter, which 
greatly aided and were confirmed by the experi- 
ments of Reed, Carroll, Lazear, and Agramonte, 
that the Stegomyia fasciata, now known as the 
Aedes (Stegomyia) calopus, was the only trans- 
mitting agent of this disease. 

In order that the methods adopted in Havana 
may be better understood, it may be advisable to 
review the status of the knowledge regarding the 
transmission of yellow fever at the time the work 

of its eradication was inaugurated in Havana, 

231 



232 The Control of Mosquitoes 

under the direction of Colonel Gorgas, in February, 
1901. 

Colonel Gorgas has treated this subject so 
comprehensively in his final report to General 
Leonard Wood that we quote from it : 

For over 200 years this disease had, at short inter- 
vals, devastated the Atlantic and Gulf coasts of the 
United States, causing great loss of life, and still 
greater financial loss, due to the entire cessation of 
commerce which occurred during the epidemic of 
1878, which affected particularly the lower Mississippi 
Valley, amounted to $100,000,000, and in years when 
there was no epidemic, quarantines had to be kept up 
against the infected regions around the Gulf of Mexico, 
which stopped almost all travel and greatly interfered 
with commerce. The United States had come to look 
upon Havana as the particular point from which 
infection was spread. Yellow fever had been con- 
tinually present in this city since 1762. Every 
month in every year during that time there have 
been some cases. In all other localities of North 
America where yellow fever occurred, it occurred 
epidemically; that is, the locality was free from the 
disease for a longer or shorter time. In places above 
the frost line, winter always puts an end to the dis- 
ease, and in localities in the tropics it always termi- 
nates after a greater or lesser period of years from the 
exhaustion of the non-immune material. 

Briefly stated, on February 1, 1901, the date of 
the commencement of anti-yellow fever work 



The Campaign in Havana 233 

based upon the theory of mosquito transmission, 
the following facts were known concerning the 
method of the transmission of this disease, and 
concerning the transmitting agent, the Stegomyia 
(Aedes) calopus, then known as Culex jasciatus 
(Fabricius) : 
The Army Medical Board had proven : 

1. That yellow fever is capable of being trans- 
mitted by the female of the mosquito now known 
as the Aedes (Stegomyia) calopus. 

2. That this mosquito must have previously 
fed on the blood of an individual sick with 
yellow fever, within the first three days of the 
disease. 

3. That an interval of twelve days or more, 
after feeding on a yellow fever patient, is necessary 
before the infected mosquito is capable of convey- 
ing the infection. 

4. That yellow fever can be produced by the 
subcutaneous injection of the blood of a yellow 
fever patient, taken in the first and second days 
of the disease. 

5. That the period of incubation of the disease 
is between forty-one hours and five days and 
seventeen hours. 

6. That "fomites" cannot convey the disease. 

7. That the Stegomyia fasciata (Stegomyia 



234 The Control of Mosquitoes 

calopus; Aedes calopus) is a house-haunting mos- 
quito. Its breeding habits, however, were not known. 

After the conclusions of the Army Medical Board 
were made known, the next problem of importance 
was the application of this knowledge to the best 
advantage. Whether it would be possible to 
eradicate, or reduce to a non-infective minimum, 
the Stegomyia calopus was then not known, and 
did not appear practicable. It was noted that the 
Aedes calopus entered and left buildings, and that 
its larvae were mostly found out of doors. It was 
generally thought that it oviposited in the open, 
under conditions similar to those suitable for 
various other species of Culicidce; and that it 
could fly long distances to reach habitations. 
The limits of its flight were not known. It had 
been observed that some Culicidce travel with air 
currents, and it was supposed by many that the 
Aedes calopus did likewise; there being no evidence 
to the contrary. 

These theories brought into the project of eradi- 
cating the Aedes calopus the question of drainage 
or filling of all the tidal and swampy land near 
Havana Bay, a very extensive area. 

Further investigation and research was carried 
on to determine the possibilities of immunizing 
the non-immune or foreign population, by subject- 



The Campaign in Havana 235 

ing them to the bites of infected Aedes calopus, in 
the hope of producing mild attacks of yellow fever, 
and thus conferring immunity. It was soon found, 
however, that the severity of the attack could not 
be controlled, and this work was abandoned. 

The board of army surgeons who verified Dr. 
Carlos Finlay's theory of the transmission of yellow 
fever by the mosquito, and made use of Dr. H. R. 
Carter's observations on time of incubation, had no 
opportunity to study the natural life history or the 
possibilities of controlling the Aedes calopus; it 
was therefore natural that they did not suggest 
the methods of procedure needful for yellow 
fever control. 

Colonel Gorgas decided to ascertain at once 
the possibility of Aedes calopus destruction on a 
large scale throughout the city, to determine what 
could be accomplished along this line. Work 
of this nature had not been attempted before, and 
all facts of importance relating to Aedes calopus 
destruction were collected as the work progressed. 
He believed that the propagation of this mosquito 
could be controlled, but few other people at that 
time believed as he did. It was the general 
opinion, with few exceptions, that an impossible 
task had been undertaken. 

The possibilities of the use of oil for purposes 



236 The Control of Mosquitoes 

of mosquito destruction and control were dis- 
covered by Dr. L. O. Howard and published by 
him as early as 1892. This information was of 
great value to the American officials in Cuba and 
has since been used extensively in many other 
parts of the world. In 1892 he published an 
article in Insect Life on the use of kerosene 
against mosquito larvae; in 1896 in Bulletin No. 
4, Bureau of Entomology, Washington, D. C, 
several pages were devoted to the subject of 
remedial measures against mosquitoes; and again 
in 1900 in Bulletin No. 25, he published "Notes 
on Mosquitoes of the United States, Giving some 
Account of their Structure and Biology, with 
Remarks and Remedies." In the latter publi- 
cation he summarized everything which had been 
done up to that time on the remedial question. 

The first systematic work of mosquito destruc- 
tion in Havana was started on March 27, 1901. 
Before this time a considerable number of adult 
mosquitoes had been destroyed by fumigation 
directed against fomites. Operations were at 
first confined to the area lying between Monserrate 
Street and Havana Bay (see map). This portion 
of the city was known as the yellow fever district. 
In this district were the commercial houses, and 
the hotels and boarding-houses the immigrants 



V 




Map of Havana: Showing the yellow fever district 



The Campaign in Havana 237 

occupied while looking for employment. It is the 
custom in Havana for clerks and employees to live 
and sleep in the stores or establishments where 
they are employed. This arrangement helped 
to make a concentration of nonimmunes, and 
hence the yellow fever cases in the locality men- 
tioned. 

In the preliminary mosquito destruction cam- 
paign one inspector and two oilers were employed 
to visit all houses and yards, and to destroy all 
mosquito-producing containers. The length of 
time necessary for the thorough inspection of the 
district above mentioned was soon determined, and 
it was then divided into sections, of such sizes that 
one inspector and two oilers could destroy or con- 
trol any mosquito breeding places in every house 
and yard in their section once a week. Later this 
system was extended throughout the entire city, 
which was divided into thirty districts. The first 
inspection of the city showed a total of 26,000 
water containers with mosquito larvae. Most of 
these were producing Aedes calopus, which were 
very numerous in the residences. 

The method of procedure was as follows: A 
list of all houses was kept at the main office. The 
district inspectors turned in each day a report 
of containers found, and an entry was made on 



238 The Control of Mosquitoes . 

a card kept for each house, thus giving a history 
of the Aedes calopus producing status of every 
house in Havana. 

The entire clerical work was accomplished by 
two men. Abbreviations were used to save time 
on reports: thus, "Real No. 3, 2B, 3T, iTna" re- 
corded the fact that at No. 3 Real Street were 
two barrels, three tanks, and one tinaja, in which 
mosquito larvae were found. Similar abbreviations 
were used for all classes of water containers. 

The inspectors* report forms were designed 
to save time, and were arranged as follows : 

District No. 5 



Date- 



Street No. B T Tna (Aljibe) Latas Pozos Misc. Name of 

House 
Tenant 



Real 


1 








Jose 
Gomez 


(i 


3 


2 3 1 






Juan 
Perez 


tt 


5 


1 




1 


Rosa 
Eave Mora 
trough 


<< 


7 








Ant Alez 
Guards Rito 
in Garden 


11 


9 




1 




Manuel 
Moreno 
1 



■(Inspector) 



The Campaign in Havana 239 

The reports were read at a glance, and rapidly 
transferred in the office to the house card show- 
ing the names of owner and tenant, with dates 
showing when mosquito larvse were found, and 
in what class of containers. These reports were 
of great use, in showing progress made in Aedes 
calopus control and preventing the continuance 
of mosquito propagation, besides furnishing valid 
evidence in courts adjudging fines. 

A system of checking the daily inspection was 
employed. Each day a trustworthy man made an 
independent inspection of several houses in every 
district, both before and following the visit of the 
district inspector. It was thus known to the 
office, beforehand, what the district inspector 
should find and report as well as whether several 
reports of the previous day's work were reason- 
ably correct. In the early stages of the campaign 
this checking was very useful, and kept the in- 
spectors up to the mark. Later, however, the 
inspectors worked more thoroughly, and the 
preinspections and reinspections seldom differed 
from the district inspectors' reports. In addition, 
the inspectors were transferred from one district 
to another at irregular intervals, and thus a check 
was obtained, and the force kept very much alive. 
The chief sanitary officer and his assistant made 



240 The Control of Mosquitoes 

frequent inspections, and kept in close touch with 
the daily work. 

It will be readily seen that such a system made 
the possible mosquito producing water containers 
disappear speedily. The number of adult Aedes 
calopus in houses quickly decreased, and to this is 
attributed the rapid disappearance of yellow fever 
from Havana. 

When the work of Aedes calopus destruction was 
commenced, it was not known how far they could 
travel or migrate, nor was it then known that they 
were exclusively container breeders. Culex with 
banded legs were seen at a distance from dwellings, 
and were reported as Aedes calopus. Little had 
been written concerning the habits and life history 
of mosquitoes up to that time, and it was vaguely 
supposed that all mosquitoes were more or less 
alike in their habits, and that all traveled long 
distances. It was not known that Aedes calopus 
do not breed in pools and puddles, or that the larvae 
of this mosquito are never found far from houses, 
unless conveyed by man. As a matter of fact, we 
occasionally find a few larvae in streams and 
ditches, but it was not known at that time that 
they had been washed out of containers. 

As the larvae destruction in houses and yards 
progressed, fewer adults were observed in dwell- 



The Campaign in Havana 241 

ings. The floors of all rooms were swept after 
each fumigation, and definite evidence obtained 
of the decrease in the number of Aedes calopus. 
Having definitely established the possibility of 
greatly reducing the number of these mosquitoes 
in Havana, it was easy to foresee that by con- 
tinued reduction very few of them need exist in 
the city ; and that it was within the bounds of 
possibility to eradicate them. 

It was found that the tenement house districts, 
locally called Casas de vicino, were the most 
difficult to control. In these houses several fami- 
lies used in common a yard, or patio, in which 
their water-holding containers were placed. It 
frequently happened that the owner of a container 
holding mosquito larvae preferred not to claim 
ownership through fear of arrest, and at times it 
was very difficult to prove who was the real owner. 

At one time many tenants hid the red earthen- 
ware jars (tinajas) containing their day's water 
supply. The coming of the inspector was signalled 
along the street and the water containers disap- 
peared as though by magic. It even became neces- 
sary to use a list of all water containers in some 
districts to avoid missing any having larvae, and 
to save time during inspection. 

The experimental work on the prophylactic 
16 



242 The Control of Mosquitoes 

inoculation of yellow fever proved unsatisfactory, 
but fortunately at that time the destruction of 
Aedes calopus had progressed far enough to show 
what could be accomplished in a few months of 
effort and persistence. 

The discovery that yellow fever propagation 
could be arrested by destroying, by fumigation, 
the Aedes calopus in the dwelling where the case 
occurred, and the houses immediately adjacent, 
showed that they do not fly long distances. This 
also indicated that even if these mosquitoes bred 
in the country, they did not find their way into the 
city in dangerous numbers. This discovery was 
very useful, as well as encouraging. 

The scheme of the work being carried out was 
strongly supported by General Leonard Wood, 
military governor of Cuba, who had full confidence 
in the ability of the chief sanitary officer. The 
people of Havana, being mostly immune, took 
small interest in yellow fever eradication, but 
submitted with little objection to the enforcement 
of the sanitary regulations. They thought that 
the Americans did not know how to control the 
situation, and had seized upon something new to 
occupy their time and make a showing. There 
was more opposition, in proportion, from foreigners 
than from natives. It was most fortunate that 



The Campaign in Havana 243 

so little opposition interfered with the campaign, 
for it must be remembered that this was all pio- 
neer work. There was much ridicule of our 
methods at that time, but fortunately this spirit 
of raillery and its pernicious influence in encour- 
aging active and passive opposition to sanitary 
methods is now decreasing. Sanitarians need 
the interest and cooperation of the general public. 

In July, 1 90 1, while the sanitary department 
was busy with yellow fever in Havana, six cases 
were reported from Santiago de las Vegas late 
one afternoon. Before daylight on the following 
morning a complete sanitary brigade was on its 
way to that town. In six weeks yellow fever was 
eradicated, and it became exceedingly difficult to 
find Aedes calopus there. 

At the instigation of Colonel Gorgas, a law was 
enacted, making it compulsory for physicians to 
report every case of yellow fever; and also all cases 
of fever, of whatever nature, occurring among 
foreigners. In locating yellow fever cases, the 
sanitary department also received assistance from 
the hospitals in Havana connected with the 
societies known as Centros. 

The larger part of the foreign population is 
Spanish, mostly unmarried men. The majority 
join one of these Centros, each of which has a 



244 The Control of Mosquitoes 

well-equipped hospital, where the members receive 
medical and hospital treatment without extra 
cost above the annual dues. Because of this 
custom, the hospitals in Havana receive most of 
the sick Spaniards, and the detection of yellow 
fever cases was greatly facilitated. All American 
"yellow fever suspects," as well as yellow fever 
patients, were sent to Las Animas Hospital, then 
under the direction of the chief sanitary officer, 
and as a rule such cases were reported in the 
earlier stages. All cases were advised to take 
hospital treatment, and most of them did so. 
When a patient preferred to remain at his resi- 
dence, it was allowed ; his room was screened, and 
the screen door was kept locked and continuously 
guarded. Only persons authorized by the chief 
sanitary officer could enter. Non-immunes were 
not allowed in the patient's rooms under any 
circumstances. As soon as a "yellow fever sus- 
pect" was reported, he was conveyed to the hospi- 
tal, or put in a screened room. Next, the history 
of his recent visits was traced, recorded, and 
verified as thoroughly as possible, in order to 
determine the source of his infection. Then 
his house and the adjacent houses were fumi- 
gated. When the patient preferred treatment at 
home, his room was not fumigated until he re- 



CURVE LINE OF DEATHS BY YELLOW EEVER 

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Chart showing irevalcnce of yellow fever in Havana, Cuba 



The Campaign in Havana 245 

covered, but all the other rooms were fumigated 
immediately, together with all places visited by 
him within a week before the onset of the disease 
and during three days following. Wherever he 
might possibly have been bitten, fumigation was 
ordered to destroy the mosquitoes which had 
infected him, or might have become infected by 
biting him. It was found important to investi- 
gate his history very thoroughly, and to verify 
and check all obtainable information. Some- 
times the history proved inexact, and certain foci 
of the infected mosquitoes were left undestroyed. 
It may also be true that walking cases of yellow 
fever occurred, which would account for so-called 
sporadic outbreaks of yellow fever. As the cam- 
paign progressed, and the mosquitoes were slowly 
but surely reduced in number, these instances 
became of less importance. 

The storehouse for all materials and apparatus 
necessary for fumigation operations on a large 
scale was established near the stables where the 
wagons and ambulances of the sanitary depart- 
ment were kept. The fumigation brigades, each 
consisting of a foreman and ten men, reported every 
morning for duty at the storehouse. In addition, 
each foreman knew where to find his men at any 
hour in case of emergencies, either during or after 



246 The Control of Mosquitoes 

working hours. Material was kept in such readi- 
ness that required quantities could be measured 
out and issued rapidly, and the brigades relied 
on for quick service at short notice. Time was 
also saved by transporting men and supplies in 
ambulances. 

When a suspected case of yellow fever was 
reported, the yellow fever commission at once 
saw the case, and if fumigation was decided upon, 
the tenants were immediately notified of the 
proposed fumigation, verbally, and by written 
notice posted on the house, stating the time work 
would be started, and the probable time of com- 
pletion. At the date and time arranged for, the 
fumigation brigade commenced operations. First, 
openings such as doors and windows were closed, 
to retain all mosquitoes within the building. As 
little disturbance as possible was made, in order 
that they should remain at rest in the rooms. 

The doorway through which supplies had to 
pass, was kept closed as much of the time as cir- 
cumstances would permit. One or two laborers 
were assigned to each room, to paste with paper 
strips all cracks, and other communications with 
the outside air, to make the room air-tight. Large 
openings were subdivided by wooden strips so 
arranged that single sheets of manilla paper would 



The Campaign in Havana 247 

reach from one piece to the other. On windy days 
a center support for each large sheet of paper was 
used. The paste was made of flour and water. 
Paper strips of different widths were kept in stock 
to expedite the work. 

The cubic contents of each room was ascertained 
to determine the number of fumigation pans 
required. 

Just before a room was finally closed, the pans 
containing the sulphur or pyrethrum were placed 
in position on the floor. Each pan was placed 
inside a larger shallow iron vessel containing 
water as a precaution against fire, in the event of 
the iron pan containing sulphur or pyrethrum 
breaking during the progress of the fumigation. 
Small boxes holding exactly one and two pounds 
of sulphur or pyrethrum powder were used for 
measuring, and it was the duty of the sanitary 
inspector in charge of the fumigation to supervise 
the placing of the fumigants in the pans, and the 
correct number of pans in each room. When as 
much of the sealing was accomplished as could be 
performed without closing the door, or other exit, 
the inspector arranged the fumigation pans in the 
most advantageous way, sprinkled the surface 
of the sulphur or pyrethrum powder with a small 
amount of wood alcohol, and then ignited the 



248 The Control of Mosquitoes 

fumigating material. After igniting the contents 
of the pans, the inspector remained in the room 
uutil he was sure that the fumigating powder was 
burning properly, and that the fires were not likely 
to go out before the f umigants were entirely con- 
sumed. A man was ready to paste up the exit 
the moment the inspector left the room. Room 
after room was treated in this manner, and hall- 
ways were treated last. The laborers engaged 
in pasting work remained at the doors long enough 
to detect escaping fumes, and repair defects in 
the sealing. 

The amount of pasting varied with the nature 
of the building treated. In some cases the entire 
wall of a room had to be covered with paper. All 
ceilings or roofs, walls, and floors were carefully 
examined, and every opening closed. Each room 
was dealt with as a separate unit, to prevent the 
formation of air currents and the traveling of fumes 
to a possible avenue of escape. During the entire 
fumigation period in Havana absolutely nothing 
was burned by the fumigation operations, although 
wooden houses might easily have caught fire. 
Every precaution was taken against accident. 
It was always necessary to make sure that no 
cats or dogs were hiding in out-of-the-way places. 

In well-built stone houses we used one pound of a 



The Campaign in Havana 249 

superior grade of pyrethrum powder per thousand 
cubic feet of air space. Sulphur, in the form of 
11 flowers of sulphur," was used in the same pro- 
portion. Where a probable leakage of fumes was 
seen to be more or less unavoidable, the quantity of 
fumigants was increased proportionally, and the 
inspectors became quite expert in gauging the 
amount required; as a matter of fact, they usually 
erred on the side of safety. 

In loosely built houses, the wind velocity had to 
be considered. Sometimes it was not advisable to 
paper the entire wall area of a house to prevent the 
leakage of fumes. Time was of value, and too 
much moving around of laborers and the manipu- 
lations incident to the papering might cause the 
mosquitoes to fly away, so that it became neces- 
sary to avoid any commotion that would result in 
sending out of doors the very infected mosquito the 
fumigation was intended to destroy. 

After all the sulphur pans were burning, and the 
last door of the house was locked and sealed, a 
notice was posted upon it stating the hour of 
closing and that of reopening by the sanitary 
department, and also that any person, other than 
the inspector in charge, who opened the door 
would be guilty of a misdemeanor and treated 
accordingly. A laborer was detailed to watch 



250 The Control of Mosquitoes 

the house, and attend to any additional pasting 
that became necessary. When the fumigation 
period had elapsed (or after three hours) , as many 
doors and windows as possible on the lower floor 
of the leeward side were first opened to let out the 
fumes. Those on the windward side were opened 
next. The inspector entered the building as soon 
as the fumes would permit, and inspected the 
pans, to see that none had been prematurely 
extinguished, and ascertain that the fumigation 
was entirely satisfactory. A repetition of fumi- 
gation was seldom necessary. Floors were then 
swept and mosquitoes carefully collected. These, 
although nearly always dead, were at once burned, 
to obviate danger from their revival. 

We had established by experimental fumigation 
that apparently dead mosquitoes revived after 
several hours' exposure to the air. 

Immediately on the return of tenants to their 
rooms, they were requested to examine their 
effects, and verify their good condition. 

All traces of paper and paste were removed after 
each fumigation, by hot water and scrubbing 
brushes where necessary. Before the fumigators 
left a house, the inspector obtained a signed state- 
ment to the effect that no articles belonging to the 
tenants were missing. Great care was taken to 



The Campaign in Havana 251 

select honest laborers, and practically no thefts 
occurred. As soon as the brigade completed 
one fumigation, the next was started. Occasion- 
ally the removal of paper, cleaning up, etc., was 
delayed for a day or two and the men were em- 
ployed at this work while other houses were closed 
during fumigation. 

In Havana houses were being fumigated before 
February, 1 901, and where pyrethrum was used 
at that time it was bought from local merchants. 
The results varied considerably. Sometimes the 
mosquitoes were killed, and at other times they 
were not. The quality of the pyrethrum varied 
greatly. Samples were obtaind from the dealers, 
and tests made to determine the quality on which 
the quantity needed for a given volume of space 
depends. 

A room at Las Animas Hospital was used for the 
fumigation tests. The cubic content was about 
1500 cubic feet. A glass transom over the door 
served as an observation window to note the effect 
of fumes on mosquitoes subjected to fumigation. 
It so happened that house flies were in the room 
during the first series of tests, and after the killing 
of Aedes calopus it was noted that the flies still 
lived. The amount of pyrethrum per 1000 cubic 
feet was increased until it was sufficient to kill the 



252 The Control of Mosquitoes 

flies. When all flies were killed, no mosquitoes re- 
mained alive. An hour longer was required to kill 
flies. Cages containing both were hung near the 
windows, close to the glass, that they might be ob- 
served through the fumigation period, and it was 
realized that the pyrethrum on the local market 
varied so much in quality as to be useless for prac- 
tical fumigation, and samples for experimental 
purposes were obtained from the United States. 

On receiving a satisfactory quality of powder, 
larger quantities were purchased, with the privilege 
of rejection if there was variation in quality as to 
generation of fumes and culicidal powers. The 
contractors kept the quality up to standard, and 
good results on a large scale were obtained. 

The experiments determined the fact that in a 
room with air-tight walls, floor, and ceiling, one 
pound of this particular grade of pyrethrum pow- 
der per thousand cubic feet and a three-hour 
exposure to the fumes was sufficient to kill all mos- 
quitoes in the room. Subsequent experiments 
proved that with any possible chance of leakage 
of the fumes, the quantity of pyrethrum used must 
be increased to allow for the leakage. Where the 
room was not reasonably air-tight and the leak- 
age was large, pyrethrum could not be relied upon, 
unless all walls, ceilings, roofs, etc., were covered 



The Campaign in Havana 253 

with paper to prevent the escape of the fumes. 
Where the leakage was extensive it was not 
effective. 

In the experimental work it was observed that 
there were most dead mosquitoes per unit of 
area near the source of light. It was also noticed 
that before they were overcome by the fumes of 
pyrethrum many of them pulled off one or more 
of their legs, but that this did not occur when 
fumigating with sulphur, tobacco, or formalde- 
hyde. Pyrethrum powder deteriorates rapidly 
when stored in a humid tropical atmosphere. 

The proprietors of tobacco warehouses and 
shops objected to pyrethrum fumigation of their 
premises because of the odor, and experiments 
were made to determine the value of tobacco 
stems as a culicide for Aedes calopus. It was 
found that the results from its use were equal to 
sulphur, and the tobacco merchants reported no 
harmful effect or deterioration of value in the 
stored tobacco and tobacco products. 

It was found that sulphur fumes injured all 
ordinary metals, unless they were protected by 
vaseline or some other greasy substance; and that 
it bleached and stained many fabrics, and stained 
certain painted surfaces. Pyrethrum only stained 
some materials slightly, but left an odor. 



254 The Control of Mosquitoes 

The results of experimental tests with the three 
substances, as obtained at Las Animas, were as 
follows : 

Pyrethrum, burned at the rate of one pound per 
thousand cubic feet in layers not greater than one 
inch in thickness, destroyed all mosquitoes in a 
well sealed air-tight room within three hours. 

Tobacco, at the rate of two pounds of stems 
(waste from Havana factories) per thousand cubic 
feet, if it all burned, killed them in three hours. 

Sulphur, at the rate of one pound per thousand 
cubic feet, was effective with an exposure of three 
hours or less. 

It is almost impossible to find a satisfactory 
grade of pyrethrum powder for fumigation pur- 
poses on the market at the present time. 

In 1906 Kendall experimented with campho- 
phenique as a fumigant; his methods and con- 
clusions are quoted: 

This substance first used in the Gulf States, has 
been tried with great success here. Berry, experi- 
menting with this mixture, found that a shallow pan 
placed upon a short piece of stove pipe formed a good 
apparatus for volatilizing the campho-phenique, and 
his method was tried here. The results were dis- 
appointing, and except for a fortunate trial of the 
fumes of this substance, they would have been dis- 
continued. It was observed that the fumes killed 



The Campaign in Havana 255 

mosquitoes with great rapidity, and that the insects 
were actually dead, not merely stupified, as is the 
case with pyrethrum. With this observation as a 
basis, a piece of apparatus, which will be described 
in great detail later on, was evolved, which has given 
excellent results in our hands. 

The apparatus was constructed with the idea of 
removing every possible source of danger which would 
occur with the mixture, as well as to provide for the 
fact that unskilled labor would have to be employed 
in practical fumigation. Cheapness is the first consid- 
eration, because it is frequently necessary to use 
large numbers of pots in fumigating large buildings. 
The use of galvanized iron, which is comparatively 
inexpensive, not only reduces this factor, but makes 
the apparatus light and not easily broken. 

To provide for the notorious lack of skill shown by 
native workmen, steps have been taken to make it 
absolutely necessary for the apparatus to be set up 
correctly. It is practically impossible to make it work 
in any other way than the correct one. Each and 
every part must occupy its correct relation to every 
other part, and of necessity this must be carried out in 
order to evolve fumes. 

In order to prevent any possible accident due to 
the catching fire of the camphor, a special fumigating 
pan has been constructed — this pan is circular in 
shape, with the edges turned downward and outward, 
making a total diameter of seven inches. In section 
it is concave, so that in reality it is a shallow bowl 
having a diameter greater than that of the stand 
upon which it is supported, with the edges turned 
down at an angle of 45 with the perpendicular. 

This shaped pan is especially adapted to the evapo- 



256 The Control of Mosquitoes 

ration of any liquid; the concavity causes the last 
remaining portions of liquid to remain in the center 
of the apparatus, where it is exposed to the hottest 
part of the flame, and the convexity presented to the 
flame permits the maximum effect of the latter for 
evaporation. Inasmuch as it is made of galvanized 
iron, hammered out of one piece, there are no joints 
to leak, or solder to melt, and the form is eminently 
suited for stacking a large number, one inside the 
other, for transportation. 

The stand of galvanized iron, riveted into a cylindri- 
cal shape, 6 inches in diameter, and 5>£ inches high. 
Near the top is a row of holes through which the hot 
air from the lamp escapes, forming a natural draft. 
This hot air acts upon the campho-phenique that 
may be near the edge of the pan, away from the direct 
action of the flame, causing rapid evaporation at 
this point as well as in the center of the pan, which 
sets into the top of the stand. The stand is supported 
on three iron legs two inches long in the clear, which 
is turned outward at right angles at the bottom one- 
half inch. This is done so that they may fit into 
appropriate straps in the bottom of the safety pan, in 
which the stand sets, to assure the correct placing 
of the latter. 

The safety pan is also made of galvanized iron 
eleven inches in diameter. In the bottom are three 
straps into which the "turned out" part of the legs 
of the stand fit. In the center of the safety pan there 
is a ring one-half inch high, three inches in diameter, 
into which the alcohol lamp fits. With the stand 
confined in its proper place by straps, the lamp like- 
wise placed in its ring, it will be seen that there is 
no possibility of any portion of the apparatus occupy- 



The Campaign in Havana 257 

ing an incorrect position. The safety pan not only 
holds the stand in position, but when half -filled 
with water forms an effective protection in case the 
alcohol lamp should begin to leak. Any lateral spurt- 
ing of the alcohol is prevented by the sides of the 
stand, and the excess alcohol would immediately be 
extinguished by the water. 

It should be mentioned in passing that the edge 
which is turned down on the fumigating pan is to 
prevent the flame of the alcohol lamp passing over 
the edge of the pan, and thus setting fire to the 
camphor and carbolic acid. 

To summarize: 

We have an apparatus consisting of four parts, a 
fumigating pan, designed to evaporate campho- 
phenique, formaldehyde, or other similar liquid, with 
an especially moulded edge designed to prevent con- 
tact of the liquid with the free flame, and to concen- 
trate the fluid as it is evaporated in such a manner that 
the last portion shall be distilled off. 

The stand is designed for steadiness, protection of 
flame from drafts, and to give rigidity to the evapo- 
rating (fumigating) pan. 

The safety pan is intended to support in their 
proper relations both the stand with its pan and the 
lamp which supplies the heat for evaporation, as well 
as a safeguard against leakage of the lamp. 

The lamp found to give the best flame, everything 
considered, is No. 15 metal spirit lamp manufactured 
by Whitall, Tatum & Co. 

The whole apparatus is made as cheaply, durably, 
and easy of transportation as possible. It is so con- 
structed as to permit its use by unskilled labor, with 
a minimum chance for damage both to itself and 



258 The Control of Mosquitoes 

to the house or other structure in which it may be 
used. 

The fumigating pan will use 8 ounces of campho- 
phenique when made in the dimensions given, namely, 
6}4 inches in diameter exclusive of the overhanging 
edge, and !}£ inches in depth in the center. With 
the alcohol lamp one-third full, ample time is given 
for complete evaporation of the liquid, with about five 
minutes to spare to allow for conditions which slow 
down the rate of evaporation. In a fairly tight house, 
with corrugated metal roof, tightly papered, campho- 
phenique has given practically perfect results. Four 
ounces of the camphor-carbolic acid mixture and sul- 
phur in amounts varying from one to three pounds per 
1000 cubic feet have been used for comparative tests. 
In several instances considerable leakage, due to the 
wind passing over the metal roof carrying off fumes, 
has occurred, but even when small leaks of known 
size have been made purposely no change in the results 
have occurred. We feel justified in saying that cam- 
pho-phenique in moderately well-built tight houses 
will give as good results as sulphur, and considering the 
extra time needed for sulphur fumigation, at an equal, 
or more probably, a lesser cost. 

In order to test the action of pyrethrum, sulphur, 
and campho-phenique upon fruit, a series of two ex- 
periments have been made under the same conditions. 
Bananas, quite ripe, mangoes, and oranges have been 
used in these experiments. The mosquitoes were not 
only placed in the customary positions in houses, but 
were also carefully hidden as much as possible in 
bunches of bananas to simulate conditions which would 
occur on ship board. The results showed that cam- 
pho-phenique is less harmful than sulphur or pyre- 



The Campaign in Havana 259 

thrum to the fruit. There was very little darkening of 
the skins of the bananas or other fruit when exposed to 
this substance, and the bananas did not taste bad. 
Several observers made these observations simultane- 
ously, tasting fruit before and after fumigation, and 
also carefully preserved controls. The indications are 
that campho-phenique is less harmful than sulphur. 
With the campho-phenique these insects were killed 
in every case; in the first trial, where the time of 
exposure was only three-quarters of an hour, one 
mosquito which was situated near the roof, where the 
fumes were practically removed by the action of the 
wind, survived for nearly half an hour, although 
it could not walk or fly. It was the only survivor 
of about eighty Aedes calopus placed in the building 
at that time. The mosquitoes hidden in the fruit 
were all killed. It is interesting to note that the 
first experiment carried out in a strong breeze, also 
resulted in a large number of survivals of mosquitoes 
in the house fumigated by sulphur, and that they 
too, were near the roof, where there was loss of fumes 
due to wind action. 

Sulphur is decidedly objectionable in many ways; 
it kills mosquitoes, however, and may be looked upon 
as a nearly perfect fumigant for these insects. Pyre- 
thrum, if it were more efficient, would do very well, 
although it leaves a decided coloration on light colored 
paint and is objectionable from the point of view of 
time consumed in fumigation, three or four hours 
being necessary, as a rule, for its combustion. Cam- 
pho-phenique in well-furnished houses (which in the 
vast majority of cases are also well-constructed) is 
very much less objectionable than either of the above, 
and it combines this factor with the comparatively 



260 The Control of Mosquitoes 

short time necessary for its evaporation, and the fact 
that it leaves a very slight residual odor, which 
quickly disappears, so that the houses are comfortably 
habitable as soon as the cleaning-up process is com- 
plete. In such cases it has given quite as good 
results as sulphur, and, considering everything, is 
much the cheapest fumigant of the three. 



CHAPTER II 

THE SITUATION ON THE ISTHMUS BEFORE SANITARY 
WORK WAS STARTED 



I 



N his Report on the Isthmian Canal, 1904, 
Colonel Gorgas stated: 



In my opinion the sanitary problems are grave. 
The question of eliminating yellow fever from an 
endemic focus has only been once before successfully 
managed, and that was at Havana. And from this 
successful work, to argue that it is easy and simple, I 
think is not warranted. The malarial work on the 
scale at Panama is entirely new. It has never been 
attempted elsewhere, and any health officer who has 
any experience in enforcing measures of individual 
prophylaxis such as will be required at Panama, can 
understand how great the difficulties of administration 
will be. Personally, I believe it can be done, and I 
approach the work with great hope of success, but I 
know that it will be neither easy nor simple, that we 
will meet with many disappointments, and have to 
modify our plans many times. 

YELLOW FEVER 

From the knowledge gained in the anti-yellow 
fever campaign in Havana, Colonel Gorgas rightly 

261 



262 The Control of Mosquitoes 

concluded that, in so far as yellow fever was con- 
cerned, the cities of Panama and Colon were the 
danger points for the Panama Canal. Both of 
these cities; Panama, with a population in 1904 
of about 25,000, and Colon, of about 4000, are 
seaports situated within a few days' travel from 
ports where yellow fever is endemic. 

Panama and Colon were infested with Aedes calo- 
pus, the conditions for the propagation of this 
species of mosquito being exceedingly favorable, 
as the climatic conditions permit mosquito breed- 
ing throughout the year. The people of Panama 
and Colon depended principally on rain water for 
their water supply. This was peddled by water- 
men, and kept in numerous vessels by house- 
holders. 

Wells, cisterns, barrels, and many other varie- 
ties of water containers, were not protected in any 
way from the female Aedes calopus seeking a 
favorable place for ovipositing. In addition 
to the various wells and water vessels, a large 
number of the houses had eave-troughs, to catch 
the rain water, and conduct it to various storage 
devices. These troughs, or gutters, many of 
them sagging, and holding water, were also favor- 
ite ovipositories of this mosquito. 

There was no systematized garbage collection. 



Conditions before Sanitation 263 

Back yards were littered with refuse of all sorts, 
as were vacant lots, alleys, and even the streets. 
This rubbish included many articles capable of 
holding water, and serving as breeding-places 
for mosquitoes. 

The difficulty of obtaining an ample and cheap 
supply of water resulted in extreme economy of 
water consumption by the people of Panama, 
especially among the poor. This economy found 
expression in the widespread custom of leaving 
dregs in the water vessels, and refilling them when 
the water ran low. To appreciate the full signi- 
ficance of this custom, it must be recalled that 
larvae of Aedes calopus remain for the greater 
portion of the time near the bottom of a vessel; 
they descend, also, with great rapidity, when 
in any way disturbed. A five-gallon bucket 
may be nearly emptied by tipping, and if 
the water is not poured out very rapidly, most 
of the Aedes calopus larvae will remain in the 
few teaspoonfuls of water left in the bottom of 
the bucket. 

Ten years ago decorative shrubs in the grounds 
of Ancon Hospital, and in private grounds in Pan- 
ama were protected from the ravages of the leaf- 
cutting ants, by surrounding each shrub with 
shallow ring-shaped dishes filled with water. 



264 The Control of Mosquitoes 

Each of these dishes was a mosquito incubator 
of a most efficient type. 

The result of all these factors favoring mos- 
quito propagation was, that the two cities har- 
bored vast numbers of these insects. The 
Aedes calopus was the commonest mosquito in 
Panama, and the mosquito bars used by some 
of the natives were intended particularly as a pro- 
tection against their annoyance. 

Turning to the records of the four years im- 
mediately preceding the inauguration of sanitary 
work on the Isthmus, the available records of 
deaths from yellow fever in the city of Panama 
show: 

109 deaths in 1900 

5 " " 1901 

202 " " 1902 

51 " " 1903 

These figures, however, indicate the yellow 
fever mortality in a population including few non- 
immunes. The accuracy of these statistics may 
also be challenged, as there was practically no 
sanitary organization in this province of Col- 
ombia, nor was the reporting of yellow fever 
compulsory. 

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Conditions before Sanitation 265 

countless breeding places in and about the houses, 
with climatic conditions particularly favorable 
to rapid and continuous development of insect 
fauna, and yellow fever foci at the very threshold, 
what would be the expectation for rapid spread of 
yellow fever were a large non-immune population 
introduced into Panama, Colon, and their vicini- 
ties? A glance at the curves on the chart will 
furnish a basis for an estimate. 

These curves were plotted from the figures 
published by Colonel Gorgas in a pamphlet issued 
in 1906, entitled: "Population and Deaths from 
Various Diseases in the City of Panama, by Months 
and Years, from November, 1883, to August, 1906. 
Number of Employees and Deaths from Various 
Diseases among Employees of the French Canal 
Companies, by Months and Years, from January, 
1 88 1, to April, 1904." The number of employees 
given is nearly correct, but the number of deaths 
from yellow fever is probably much below the cor- 
rect number. The only mortality statistics availa- 
ble are those of Ancon Hospital, and many cases of 
yellow fever never found their way into the hospital, 
either dying before they could be sent there, or re- 
maining outside because the contractors were more 
or less reluctant to pay for the treatment of their 
employees. After carefully investigating various 



266 The Control of Mosquitoes 

sources of information, the authors believe that 
the number of cases given in this table approaches 
the true mortality more nearly if multiplied by 
two. Basing the estimate on a case mortality rate 
°f 33% with an average population of 15,000 
in 1886, the number of deaths given in the statis- 
tics is corrected to the more probable number 616 
(308X2); the cases developed during that year 
must have exceeded 1500 or ten per cent, of the 
entire working force. 

The year 1886 was the fifth of the French occu- 
pancy, the year during which the work was at its 
height, and when the number of non-immunes 
was comparatively high. This year can be taken 
as a fair basis for an estimate of the mortality from 
yellow fever that would probably have had to be 
faced by the American forces on the Canal. The 
average force employed by the United States 
on the Canal was 35,000 to 40,000 mostly non- 
immune to yellow fever. With a mortality of 
four per cent, per annum, as was the case with 
the French force in 1886, we should have lost 
more than 1400 men each year from yellow 
fever alone! 

The curves on the chart show a very interesting 
phenomenon, in the rapid rise of yellow fever with 
the influx of non-immunes; this rise taking place 



Conditions before Sanitation 267 

at a swiftly accelerating rate; then the decline as 
the non-immunes either die or recover from 
the disease; and the subsidence of the epidemic 
as the non-immune material is exhausted. 



CHAPTER III 

GEOGRAPHY, METEOROLOGY, ETC., AND THEIR 
BEARING ON THE PRESENCE OF AEDES CALOPUS 

npHE Canal Zone is a narrow strip of land ten 
* miles wide and approximately forty-eight 
miles long, situated entirely within the torrid zone. 
Its northern boundary is in latitude 9 24/ 40" N. 
(vicinity of Punta Mala Remo). Its southern- 
most latitude is 8° 54' 40'' N. (Punta Bruja). 
The seasons are well marked: a rainy season of 
nearly eight months' duration and a dry season 
of about four months, January to April. 

The mean annual temperature is approximately 
8o°F. 

The extreme range of temperature is between 
68° and 97 F. 

The climate and temperature are favorable to 
mosquito propagation the year round. 

In 1904 when the Canal Zone was ceded by the 
Republic of Panama to the United States, it con- 
tained a number of villages and small settlements ; 

268 



Geography and Meteorology 269 

two of tnese were at the ocean terminals of the 
Canal, Cristobal on the Atlantic, and La Boca, re- 
cently renamed Balboa, on the Pacific. In addition 
to these were the cities of Colon and Panama, which 
although not in the Canal Zone politically, are yet 
geographically so, and were placed within the san- 
itary jurisdiction of the United States by treaty. 

Colon and Cristobal are situated on Manzanillo 
Island, a flat marshy piece of land the elevation of 
which is approximately four feet above mean tide. 
This island is largely a coral formation covered 
with a layer of soil. There are no rivers or springs 
on the island, and no wells. Formerly the only 
source of water supply for Colon was rain water 
and fortunately the precipitation in this locality 
is very great, averaging 120 inches annually. 
Some water was brought into Colon by rail and 
stored for use. The towns in the Canal Zone de- 
pended for their supply on adjacent rivers, streams, 
and springs, which are plentiful in the Zone. Pan- 
ama, Ancon, and Balboa (La Boca) are situated 
at the southern extremity of the Canal. The 
rainfall there is far less than on the Atlantic slope, 
averaging about seventy inches per annum. The 
stored rain water was therefore supplemented by 
wells and aqueducts carrying surface and subsoil 
water, with tanks for storage. 



270 The Control of Mosquitoes 

The owners of the aqueducts and wells sold the 
water to carriers, who in turn sold it to the con- 
sumer. The price of water sold from the carts was 
usually five cents for a five-gallon can and some- 
times doubled toward the end of the dry season. 

It will be seen from the foregoing that climatic 
and topographical conditions are very favorable 
to Aedes calopus in the Canal Zone, and espe- 
cially in the cities of Panama and Colon. In the 
adjacent settlements of Balboa, Ancon and Cristo- 
bal, where scarcity of water compelled each house- 
hold to husband to the utmost any supply 
obtainable, the result was that these cities and 
their environs harbored thousands of ideal mos- 
quito breeding places. 



CHAPTER IV 

THE FIRST SANITARY WORK DONE AT PANAMA — ITS 

PURPOSE 

IN July of 1904, when Colonel Gorgas and his 

* assistants undertook the sanitation of the 

Isthmus, it was not definitely known that yellow 

fever was present. The authorities were not aware 

of any cases. At least none had been reported in 

the months of February, March, or April, 1904, 

and there was reasonable doubt regarding the 

diagnosis of the two cases reported in May and 

June. The number of non-immunes was relatively 

small in proportion to the native population. It 

was understood, of course, that as soon as the 

percentage of non-immunes to total population 

increased, if yellow fever were present, a number 

of cases would develop, unless the chief sanitary 

officer had the necessary organization, police 

power, supplies, appropriations, and power to 

enforce the sanitary regulations; in brief, that 

unless the proper means were used to combat 

271 



272 The Control of Mosquitoes 

the disease in its incipience, conditions would be 
favorable for an epidemic as soon as enough 
American non-immunes arrived. 

Colonel Gorgas earnestly endeavored to have 
a properly qualified representative of the sanitary 
department on duty in the United States, so that 
all supplies necessary for the control of yellow 
fever and operation of the hospitals might be 
properly selected, expeditiously purchased, in- 
spected, and rushed to the Isthmus without delay. 
Delay, he foresaw, might result in many deaths 
among Americans, and cause a longer and more 
expensive yellow fever campaign. His recom- 
mendations regarding this matter were, unfortu- 
nately, not approved. 

The treaty between the United States and the 
Republic of Panama contained the following 
clauses : 

The Republic of Panama agrees that the cities of 
Panama and Colon shall comply in perpetuity with 
the sanitary ordinances, whether of a preventive or 
curative character, prescribed by the United States; 
and in case the government of Panama is unable or 
fails in its duty to enforce this compliance by the 
cities of Panama and Colon with the sanitary ordi- 
nances of the United States, the Republic of Panama 
grants to the United States the right and authority to 
enforce the same. 



First Sanitary Work 273 

In accordance with the terms of the treaty, the 
Republic of Panama agreed that the sanitation of 
the cities of Panama and Colon should be directed 
by the chief sanitary officer of the Isthmian Canal 
Commission. At the request of the latter, the 
Mayors (Alcaldes) of the cities of Panama and 
Colon issued the following ordinance: 

Ordinance Number 6. Under the authority granted 
by decree No. 25, of July 8, 1904, issued by the Presi- 
dent of the Republic of Panama, the following sani- 
tary regulation is issued: 

Breeding of mosquito larvae (wigglers) is prohib- 
ited within the limits of the city of Panama and the 
occupants of premises will be held accountable for 
violation of this regulation. 

All cisterns, water barrels, and deposits of fresh 
water must be made mosquito-proof, and all occupants 
of premises must see that other deposits of water are so 
arranged that mosquitoes cannot breed in them. 

Violation of this ordinance will make the offenders 
liable to a fine of five dollars gold. 

(Signed) W. C. Gorgas, 

Chief Sanitary Officer. 

Previous to sailing for the Isthmus, the chief 
sanitary officer called the attention of the Isthmian 
Canal Commission to the advisability of immedi- 
ately obtaining experienced assistants and sani- 
tary supplies. He submitted an itemized list 

showing what was required. Although the 

18 



274 The Control of Mosquitoes 

estimated cost was not large, the amount allowed 
him was below the sum asked for. 

The first house to house inspection of the city of 
Panama showed that Aedes calopus larvae existed 
at practically every house in town. Adults of the 
species were plentiful everywhere, and everyone 
who could afford it used mosquito bars. Foreign- 
ers found it impossible to sleep comfortably 
without a mosquito bar, and one could not sit 
down even in the daytime without being annoyed. 

The ice supply was limited and ice was expensive, 
five dollars per hundred pounds, when obtainable. 
The natives cooled water by keeping a supply 
indoors in semi-porous earthenware vessels, called 
tinajas. In these larvae thrived in great numbers 
inside the houses, as well as in the barrels, etc., in 
the patios. 

After the first inspection of the town was com- 
pleted, and proper notices published in the press 
concerning the proposed campaign against mos- 
quitoes, a second inspection was made, and at 
all places where mosquito larvae were found, the 
owners of the water containers were requested to 
assist the sanitary officers by complying with 
Ordinance Number 6. The number of containers 
with mosquito larvae was reduced. A written notice 
was next sent out, inviting the attention of those 



First Sanitary Work 275 

who were violating the ordinance to the fact that 
they would be liable to prosecution, in accord- 
ance with the ordinance; and in every way 
possible, a strong effort was made to obtain the 
peopled support. 

Subsequent inspection showing many delin- 
quents, their names and addresses were forwarded 
to the mayor of the city, who had authority to 
impose fines. Practically no fines were imposed, 
and the people of the lower class, finding the ordi- 
nance not insisted on by the mayor, gave it little 
attention. Each week a list of citizens violating 
the ordinance during that week was duly for- 
warded to the mayor. It is not known if any na- 
tives were fined although rumor had it that some 
foreigners were. 

The number of American employees and foreign 
population increased as time passed. Every 
means was used to induce the Mayor to enforce 
the law, and render the work effective, but without 
result. 

The first case of yellow fever occurred at the San 
Tomas Hospital on November 21, 1904. The 
patient was an Italian, and came from a restau- 
rant at Santa Ana Plaza, near the center of the 
town. The case was at once isolated in the mos- 
quito-proof ward of the hospital. During De- 



276 The Control of Mosquitoes 

cember six cases developed. There were no deaths. 
No cases appeared among Canal employees in 
1904. In January, 1905, eight more cases were 
reported, two resulting fatally. Three cases of 
yellow fever developed on board the steamship 
Dora j en route to Havana from Colon. They 
were Italians, members of an opera troupe, and 
contracted yellow fever while sojourning in Colon. 
Two of these cases terminated fatally. 

An outbreak of yellow fever occurred on the 
U. S. Cruiser Boston, while she was at target prac- 
tice at Chame Point, in Panama Bay. The Boston 
was in Panama harbor during November, 1904. 
Six cases developed on board the ship. The vessel 
was thoroughly fumigated, and no further cases 
followed. 

It was evident that strenuous measures were 
needed to control the situation; but little help 
could be counted on from the local native authori- 
ties, and with the constantly increasing number 
of non-immune arrivals, yellow fever cases would 
increase in number, and assume the form of a 
serious epidemic. The inspection force was 
therefore increased to enable the inspection of all 
houses once a week. All containers found with 
mosquito larvae were washed out. Tanks and 
larger vessels that could not be freed from larvae 



First Sanitary Work 277 

in this manner were treated with oil. Sufficient 
oil was used to cover the water surface com- 
pletely. As the force became more experienced, 
better control was established. 

In the early part of 1905 there was a large 
number of non-immunes in the city of Panama, 
and it became necessary to work with increased 
vigor, because, even with a greatly reduced num- 
ber of Aedes calopus, the chances for the spread of 
yellow fever increased. 

The fumigation work proved the marked effects 
that elimination of the containers had made on the 
eradication of Aedes calopus by the decreased 
number of dead insects found after fumigation. 
Ultimately we controlled the situation to the 
extent that but one per cent, of the houses were 
producing larvae, and inspection work caused a 
large percentage of larvae to be destroyed. One of 
the difficulties was in locating hidden containers. 
A few of these in a single block of houses were 
sufficient to enable Aedes calopus to reach other 
houses and decrease the efficiency of the work. 
As the ordinance was not properly supported, it 
became evident that the sanitary department 
would be obliged to undertake the task of screen- 
ing, and making inaccessible to mosquitoes, all 
water barrels, tanks, cisterns, wells, etc. This 



278 The Control of Mosquitoes 

work had to be done thoroughly, or was of practi- 
cally no value. 

The city was divided into eleven districts for 
purposes of house to house inspection for locating 
and eradicating breeding places. An inspector 
was assigned to each district. He rendered daily 
reports of the status of each house visited, with 
regard to water containers. The force employed 
was composed largely of natives, who did not at 
first realize the importance of their work. They 
were fully instructed as to their duties, and their 
work was checked. When doubt arose as to the 
quality of the inspector's work, half a dozen of the 
houses in his district were inspected the day before 
he visited them, and his reports were checked 
against the special inspection reports. 

Then, again, the districts were changed at 
frequent intervals, which served as a check on 
each man's work, so that before long each inspector 
either became efficient, or was replaced by a better 
man. The reason for reinspection and changing 
of inspectors was to determine the amount of 
time required for inspecting the districts, and to 
teach the men not to miss a single container. 
Every man was checked, and had to work with 
about the same rapidity, cover as much ground, 
and show as thorough results as the most efficient 



First Sanitary Work 279 

man on the force. The scheme worked out well, 
although at first, in the weeding-out process, many- 
changes occurred in the force. 

Reinspection was continued throughout the 
entire campaign, to prevent unsatisfactory condi- 
tions in any district. A record of every house 
was kept, and those in which mosquito larvae 
were apt to be found most frequently became 
known to the department, and were watched more 
closely. These house records showed the number 
of wells, tanks, cisterns, barrels, etc., within each. 
In order to eradicate these sources of mosquito 
production, a force of carpenters was employed 
to make mosquito-proof covers for them, and 
another gang to attach the covers to the containers. 
After they were placed, it became the duty of 
the inspectors to report any that had been detached 
or tampered with. When a cover was taken off 
a barrel or well, the water container was considered 
a menace to health, and was removed or destroyed. 
All containers not absolutely necessary were re- 
moved, and properly disposed of. The exami- 
nation of the larger water containers, tinajas, 
open-top stone filters, etc., in dark corners of the 
houses, consumed much time. These vessels 
were listed, that none might be missed, and 
inspectors had to report the condition of each 



280 The Control of Mosquitoes 

one at every inspection. House tenants hid 
containers, and could never understand why an 
inspector who had missed a container one day 
always came in search of it the following day. A 
small acetylene lamp or an electric flash lamp 
was used to determine the presence of mosquito 
larvae in large containers in dark places. 

The non-immune residence sections were located 
in three limited areas, and especial care was taken 
in these localities. Most of the Americans in 
Panama in 1905 were employed by the Isthmian 
Canal Commission, and the greater part of them 
worked in what was then known as the "Canal 
Building," which occupies an entire block and is 
three stories high. Naturally, this building, if 
it contained infected mosquitoes, would become 
an important focus for the spread of yellow fever. 
To prevent such an occurrence, two inspections for 
water containers were made weekly, and the entire 
building was fumigated once every fortnight. It 
was found that the screened doors' leading onto 
the verandas were propped open or held open by 
the janitors, and that mosquitoes actually gained 
access to the building through these doors. In 
order to prevent this, the department of sanita- 
tion placed a lock on each veranda door, and kept 
them locked, with the keys in charge of one re- 



First Sanitary Work 281 

sponsible man. Only one entrance door to the 
building was allowed, and a watchman was 
stationed continuously at that door to see that it 
was not left open a moment longer than necessary. 

It was unfortunate that greater power was not 
given to the chief sanitary officer, to enable him to 
prosecute the yellow fever campaign more rapidly. 
Under the organization then in power, he was often 
limited to making recommendations, which were 
not always carried into effect. Those inexperi- 
enced in matters pertaining to yellow fever control 
cannot and should not be expected to take part 
in the work of its suppression, unless they are sub- 
ject to the orders and under the direct control of 
the officer charged with the eradication of yellow 
fever. 

A case in point was that of the so-called Canal 
Building in Panama, the original headquarters of 
the Canal force. There was much delay in having 
the building properly screened. The architect who 
had charge of this matter was overworked, and 
busy with plans and estimates for the repair and 
construction of buildings all along the line of the 
Canal. Work was waiting for all the men avail- 
able, and there was not enough room to accommo- 
date the needed force. Of course, the architect's 
first consideration was to provide housing facil- 



282 The Control of Mosquitoes 

ities. The sanitary department thought it of 
prime importance to have the building, which 
was located in an infected area, properly screened, 
as it was used almost exclusively by non-immunes. 
The importance of neglecting some other work, if 
need be, and attending immediately to the screen- 
ing of the Canal Building was brought to the atten- 
tion of the architect time and again, but he thought 
the matter of secondary importance compared with 
the work he was doing elsewhere, and the screening 
was delayed. The architect even joked about the 
fuss made over the screening. He had not lived in 
tropical America before, and had but little faith 
in modern ideas pertaining to yellow fever trans- 
mission and control. This able and efficient 
young man was among the first Americans who 
died of yellow fever, contracted in the building he 
had not screened, and other employees in the 
offices in the same building also contracted the 
disease. It cannot be said that the architect 
was responsible for his own death and the death of 
the others : the source of the trouble was higher. 
When the power of the sanitary officer is limited, 
the efficiency and speed in obtaining results will 
always be limited proportionally, and often with 
very serious results. 

The non-immune population lived in Panama 



First Sanitary Work 283 

in three well-defined areas: the Italian colony 
on Malambo Street, the Americans near Central 
Park, and a considerable number near Plaza 
Santa Ana. Many Americans lived in the Ancon 
Hospital Reservation. The buildings in these 
areas most likely to harbor yellow fever cases 
were fumigated every two weeks, to eradicate any 
infected mosquitoes that might be present. It 
is remarkable that in Ancon Hospital, where most 
of the yellow fever cases were cared for, no cases 
of yellow fever were contracted. The reason for 
this was, that the hospital grounds were under 
the direct control of the chief sanitary officer, 
and the few adult Aedes calopus remaining there 
were not allowed to enter the buildings after 
they were once screened. Everybody in the 
hospital cooperated to prevent them from getting 
a foothold, and all were interested in the results 
of the anti-mosquito campaign. 

It was often difficult to locate the house where a 
yellow fever suspect had been bitten by an infected 
mosquito. In instances of yellow fever "walking 
cases," not infrequent in the early stages of the 
disease, the source of the infection may never be 
located. 

When a case or a suspected case of yellow fever 
was reported we obtained from him as promptly 



284 The Control of Mosquitoes 

as possible a list of the places he had frequented 
(so far as he could remember), and a list of his 
friends or relatives. We questioned them in turn 
to make the history of the patient's previous move- 
ments as exact as possible. We often received con- 
flicting testimony, and the patient in many cases 
was not in a condition to remember where he had 
been at the time of infection, or since. It was 
very important to obtain this information, so that 
effective measures might be taken to destroy by 
fumigation the infected mosquitoes that had 
inoculated the patient, and that the Aedes calopus 
which had bitten him during the first three days 
of the disease be destroyed, before they in turn 
should become infectious and bite non-immunes. 
In some cases the patients were delirious, and 
gave no clue to their history. In a few cases 
false information was given and the much-needed 
facts withheld. The missing of one link in the 
chain of evidence meant leaving some infected 
mosquitoes alive, with the possibility of secondary 
cases. As some cases occurred which could not 
be traced to previous known sources of infection, 
it was decided to fumigate all houses in the city 
of Panama in succession as rapidly as possible. 
The fumigation brigade was increased, and the 
work pushed as rapidly as conditions would per- 







Part of the Panama fumigation brigade 



First Sanitary Work 285 

mit. All the houses in one or more blocks were 
fumigated in a single day. Block after block was 
fumigated from one end of the town to the other. 
At this time we had a number of cases of yellow 
fever, and though the myriads of mosquitoes 
were greatly reduced, the comparatively few 
remaining, together with enough cases of yellow 
fever and a large non-immune population, made 
transmission easy. 

The following measures were adopted to insure 
knowledge of every case as rapidly as possible. 

Reporting of suspected cases of yellow fever, 
and of all fevers among non-immunes, was made 
compulsory by the following section of the sani- 
tary rules and regulations for the cities of Panama 
and Colon: 

Contagious Diseases. 

Section 10. Every physician, druggist, school 
teacher, clergyman, midwife, nurse, and every head of 
a family, having knowledge of any case of the follow- 
ing named diseases, shall immediately report the same 
to the Health Officer: Asiatic cholera, yellow fever, 
typhus fever, smallpox, plague, dysentery, diphtheria, 
and membranous croup. 

All hotels, etc., were required to keep a register, 
and a physician visited every hotel and boarding 
house daily to ascertain whether any non-immune 



286 The Control of Mosquitoes 

residents were sick. In order to prevent the 
concealing of cases, patients were not compelled 
to go to hospital, but could remain at their resi- 
dences and be treated by their family physicians 
under conditions specified by the chief sanitary 
officer. In addition, a reward of $50.00 was paid 
to the first person reporting a case of illness which 
was subsequently diagnosed by the Yellow Fever 
Board as yellow fever. 

When a suspected case of yellow fever was 
reported, the patient and his relatives or friends 
were interviewed, and an effort made to transfer 
him to Ancon Hospital. Almost all Americans 
acceded. Where the patient preferred to remain 
at his home, his room was at once made mosquito- 
proof. The windows and all doorways except 
one were screened with immovable screens. The 
single entrance door was fitted with a vestibule 
provided with two screened doors. Both these 
doors were fitted with strong springs to make 
them self-closing. The outer door was kept 
locked, and the key was in charge of a guard 
employed by the sanitary department. These 
guards were on duty in eight-hour shifts, that 
the door might not be left unguarded until the 
patient was removed from the room. At the 
termination of the case his room was fumigated, 




~9 . 










w -*~* <* m "i" - r 



Screened vestibule door 



First Sanitary Work 287 

the adjacent rooms and houses having already 
been so treated. 

No non-immunes were allowed in the patient's 
room. His physician, nurse, and possibly one or 
more immune friends, with the approval of the 
chief sanitary officer, were allowed to enter the 
screened room. No one could pass the guard 
without written authority. 

In Ancon Hospital two wards and several pri- 
vate rooms were used solely for yellow fever sus- 
pects. To enter the wards it was necessary to 
pass through a vestibule provided with three 
screened doors. A pan of pyrethrum powder 
was kept burning constantly between the last 
two doors, and a guard was always present to see 
that the doors were opened and closed rapidly. 
The nurses and physicians learned to pass through 
the doors quickly and inspected the wards daily 
for Aedes calopus. The windows were screened 
on both the inside and outside and examined 
twice daily for defects. The buildings and the 
grounds in the vicinity of the hospital were fre- 
quently inspected for possible water containers. 

All of the nurses and many of the physicians 
were non-immunes, but no case of yellow fever 
developed among those caring for the patients and 
living in the hospital grounds, although at times 



288 The Control of Mosquitoes 

there were as many as 200 Americans living there. 
All suspects arriving at the hospital were placed 
in beds under large screened cages located within 
the screened wards, and the yellow fever cases 
were kept in these cages during the first five 
days of their illness. These precautions made it 
necessary for a mosquito to pass through a cloud 
of smoke and four screened doors before it could 
reach a patient, and then escape through a door 
into the ward, where it must survive a twelve 
days' search for mosquitoes before attacking a non- 
immune. It was almost impossible for such a 
combination to happen, and it never happened. 

When the yellow fever wards were first fitted 
up, no metal screening was available. Cotton 
mosquito bar had to be used for screening the 
buildings, and with care and the precautions taken, 
it gave satisfactory results. Its fragile nature 
renders it unserviceable for extensive use, but in an 
emergency it can serve, as at Ancon. 

With the installation of water and sewerage 
systems in Panama, it became unnecessary to use 
water containers for storage purposes, and as fast 
as water was installed in each house, the tanks, 
barrels, cisterns, etc., were removed or destroyed. 
This assisted to a very large extent in eliminating 
mosquitoes. But public water and sewer systems 




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First Sanitary Work 



289 



alone do not rid a Central American community 
of them. Rain water is soft, and people were 
accustomed to use it. The widespread custom 




HEAVY STRAP IRON SUPPORT 

A firmly supported eave-trough. 



of collecting and keeping it was difficult to 
eradicate. 

A'edes calopus breeding also occurred in the 
eave- troughs, which sagged, and were difficult to 



19 



290 The Control of Mosquitoes 

inspect. Eventually they were all removed. The 
tinajas are still used, but as water costs much 
less than formerly, they are emptied more fre- 
quently, and are less dangerous. 

In localities where there is no available water 
supply other than rain water collected by roofs 
of buildings, it may be absolutely essential to use 
eave-troughs to obtain all the water possible for 
storage and future use. 

If eave-troughs are used for that purpose they 
should be made of galvanized iron of sufficient 
thickness to prevent sagging, have a good slope, 
and be securely attached to the roof. It is neces- 
sary to have the points of support as close together 
as possible. They should be arranged to permit 
inspection without leaning heavy ladders against 
them. Eave-troughs are convenient but nearly 
all towns where the yellow fever mosquito is 
found could do without them. 

In an anti-yellow fever campaign, it is not safe 
to rely on fumigation only, for we cannot be sure 
that all the places in which infected mosquitoes 
exist have been fumigated. It is only possible 
to accomplish a certain amount of fumigation in 
one day, and meanwhile mosquitoes in the adja- 
cent unfumigated buildings may return. It is 
evident that fumigating on a wholesale scale, i.e., 







ft 



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o 



o 
o 



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u 

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a> 

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<u " 
+j 
u 
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a 
a 

to 

a 

In 



First Sanitary Work 291 

fumigating all houses in a town or village, will not 
necessarily kill all the mosquitoes present in and 
about the houses, though probably the greater part 
may be destroyed. It is surprising how soon they 
will disappear, if all the water containers and 
places in which they oviposit are removed. We 
believe that the thorough and rapid destruction 
or protection of all possible containers and breed- 
ing places is the most effective method of yellow 
fever control, and that where the health officer is 
supported by the residents, Aedes calopus eradi- 
cation is quite possible. The campaign at San- 
tiago de las Vegas, Cuba, proved this beyond 
doubt. 

It is not absolutely necessary to eradicate all 
Aedes calopus in order to eradicate yellow fever. 
It is only necessary to reduce the number of adults 
sufficiently to prevent their presence in the vicin- 
ity of the places visited by non-immunes. 

The matter can be stated thus: In order to 
eradicate yellow fever from a given community it 
is necessary to reduce the number of Aedes calopus 
to such a minority that there is no opportunity for 
their biting an infected case during the first three 
days of the disease, and surviving twelve days 
after. Of course, the nearer the reduction reaches 
complete eradication the better, especially in re- 



292 The Control of Mosquitoes 

gard to the reintroduction of the disease at some 
future time. 

When the reduction of Aedes calopus has 
reached a certain stage, the chance of a person 
being bitten becomes so small that transmission 
of fever stops. Yellow fever was eradicated 
in the epidemic at Havana, Santiago, and other 
towns and villages in Cuba, as well as in the Canal 
Zone and the cities of Panama and Colon, when the 
number of Aedes calopus present was much higher 
than now. Since the last case of local origin in 
1906, on several occasions imported cases have 
gained access to, and actually been at large in 
Panama and Colon, without producing secondary 
cases; because the number of adult Aedes calopus 
is so small that there are almost no chances of 
completing the chain necessary for the transmis- 
sion : a patient being bitten, this particular insect 
surviving twelve days, and then biting a non- 
immune. In some settlements in the Canal Zone 
Aedes calopus are now seldom seen. 

It must be remembered, however, that but a 
short time is needed to reintroduce this species 
of mosquito, and that if conditions are allowed to 
become favorable, it will both multiply and spread 
over a populated area with great rapidity. 



CHAPTER V 

THE ANTI-YELLOW FEVER CAMPAIGN AND ITS 

RESULTS 

AFTER the arrival of Colonel Gorgas and his 
assistants on the Isthmus, preparations for 
the campaign were begun before the first case 
of yellow fever was reported. As rapidly as 
possible all barrels used for storing water were 
made mosquito-proof. Wooden barrel covers 
with wire-gauze protected openings were made 
and shipped to the different villages. These 
were nailed to the barrel tops by the sanitary 
department, to leave no doubt of their remaining 
mosquito-proof. An inch or so below the top 
of the barrel an augur hole was made, and mos- 
quito wire nailed over it. This hole was intended 
for an overflow, to prevent the water from coming 
in contact with the wire-gauze covered opening 
in the top, and thus inviting ovipositing. 

The covers were made by fastening together two 
boards about twelve by twenty-four inches, leaving 

293 



294 The Control of Mosquitoes 

an opening four inches square when the boards 
were fastened together. This opening was covered 
with a square of eighteen mesh copper wire 
gauze, protected by placing above it a square of 
half-inch mesh galvanized iron wire, and the 
whole fastened in place with wooden strips. A 
wooden spigot was inserted near the bottom of the 
barrel. 

It was necessary to see that the edge of the 
barrel was "true, " and when not, to correct it; 
otherwise the cover would not fit snugly and the 
entire work would be useless. 

Prompt results in mosquito control may be 
obtained by making water barrels non-accessible 
to mosquitoes in the following manner. Muslin 
or sacking is fastened securely over the top of 
the barrel, and also over a one-inch overflow hole 
six inches below the top. The water is obtained 
from a wood or metal faucet. 

The use of this scheme on a large scale neces- 
sitates much careful inspection and also cooper- 
ation on the part of the house tenant. When 
careless people remove and replace this barrel 
covering, the barrel may be left temporarily 
uncovered and mosquitoes propagated and liber- 
ated unknown to those conducting the anti- 
mosquito campaign. The cloth should be kept 



Campaign and Results 295 

free from holes and be fastened to the top of the 
barrel with strong wire. The twisted portion of 
the wire must be so sealed that it cannot be 
unfastened or replaced without the fact being 
easily detected. Although this method of control 
is often not satisfactory, it may sometimes be 
helpful. It is rapidly installed, inexpensive, and 
may serve temporary purposes. 

At first the natives took off the covers, and did 
not replace them properly. When taken to task 
about this, they professed a desire to clean the 
barrels. Observation proved that before the 
barrels had been covered they had seldom been 
washed out ; then it appeared that the people were 
so accustomed to dipping out the water, they did 
not want to use the spigots. This practice was 
soon stopped. 

When the sanitary work was started, the houses 
in the villages were mostly surrounded by jungles 
or high grass. All bottles, cans, and other poten- 
tial water containers and rubbish were thrown out 
of doors, and hidden by the vegetation. It was 
therefore necessary to do much clearing of vege- 
tation and collecting of water containers. Within 
a week or two after this work was completed 
the grass was high again. Much effort was 
required to make tenants place useless water 



296 The Control of Mosquitoes 

containers within the garbage cans. Where the 
houses were close together it was difficult for the 
inspectors to find the guilty individual. Appar- 
ently it was not easy for the people to change their 
habits. It was found necessary to keep the grass 
short near houses, so that water containers could 
be easily found. 

The interiors of all houses were inspected for 
water containers, which disappeared as the inspec- 
tor approached. Usually the tenants emptied 
water vessels at the back door, while the inspec- 
tor was entering at the front. 

In 1904 houses in the Canal Zone were not 
screened. Each American employee was furnished 
with a mosquito bar, but they were not used in a 
way to make biting impossible. Even bars 
that were intact, when improperly tucked in 
around the mattresses, proved ineffective. Many 
people roll in bed, and thus come in contact with 
the mosquito bar while asleep; and mosquitoes 
bite through the bar and the sleeper may be un- 
aware of it. It was also found that bars were 
easily torn, and seldom promptly repaired. In 
order to make the bars effective, the sanitary 
department undertook to keep those of canal 
employees in repair, free of charge. 

After the houses were screened, and the number 



Campaign and Results 297 

of adult Aides calopus became very small, no more 
bars were used. At the present time they are 
unnecessary and are not used by people in the 
Canal Zone. 

We learned by experience that when mosquito 
bars must be used, the following precautions should 
be carefully observed. 

1. The bar should be ample in size, and made 
of durable material of considerable tensile strength. 

2. It should be carefully tucked under the 
mattress, or if no mattress is used, under three 
sides of a piece of matting laid on the bed or cot. 
Just before entering the bed, the interior of the 
bar should be carefully searched for mosquitoes, 
and those within destroyed. When a mosquito 
is hidden within a net, a small electric flash lamp 
helps to discover it. 

3. Enter the bed quickly, disturbing the bar 
as little as possible. 

4. Tuck in the bar carefully on the side through 
which you enter. 

5. Sleep in a wide bed, and cultivate the habit 
of sleeping quietly in the middle of it. 

We knew that yellow fever would occur at 
Panama and Colon as soon as the percentage of 
non-immune population was sufficiently high to 
favor its propagation. As it was proposed to 



298 The Control of Mosquitoes 

concentrate the newly arriving Americans at La 
Boca, Ancon, Culebra, and Gorgona, a strong 
effort was made to control the Aedes calopus 
production at these villages as rapidly as possible. 
It was expected that the employees quartered 
in these settlements would visit the terminal 
cities, and that some of them would contract the 
fever. Every effort was made to prevent trans- 
mission of yellow fever from any of those who 
might have become infected in Panama or Colon, 
to others living at the villages mentioned. The 
first cases of yellow fever in the Canal Zone de- 
veloped at Culebra, Balboa, and Corozal. All 
Americans living at Corozal worked in the city 
of Panama and none of the residences of the 
employees were screened when yellow fever first 
appeared. When the first cases occurred, the 
history of every patient was rapidly obtained. 
All places visited by them since their infection, 
and where they might have become infected, were 
fumigated with sulphur, as were also all adjacent 
houses. The patients whenever possible were 
removed to the yellow fever wards at Ancon 
Hospital. 

The fumigation was at first a difficult task to 
accomplish. The sanitary department was allowed 
to pay only the lowest rate of wages current, and 



Campaign and Results 299 

consequently only poor and unintelligent labor 
could be obtained. Any intelligent laborer could 
find employment elsewhere at a higher rate of 
pay. Even the men employed for scavenging and 
ditching were used as a fumigation squad. Some 
of them had not enough sense to hurry while 
working in sulphur fumes. It was not unusual 
for them to leave us while fumigations were in 
progress, for working in sulphur fumes day after 
day at the lowest rate of wages was not attractive. 
At that time in the Canal Zone a laborer could 
find work anywhere else for the asking and often 
at higher wages. The sanitary inspectors deserve 
great credit for the manner in which they won 
success in spite of the numerous difficulties they 
faced. Apparently many of the laborers had 
never moved with celerity before in their lives, 
and some of them could not even climb a ladder. 
Otheis who went into the rooms to open windows 
after fumigation did not understand enough to 
return quickly, and were dragged out in a state of 
collapse. This was the only class of labor allowed 
the sanitary department. We had to use it, and 
succeed or fail. 

Many of the native houses were so loosely built, 
and so full of cracks, that it was necessary to paste 
paper over the outside of the greater part of them, 



300 The Control of Mosquitoes 

and contend with leaks in the roofs also. At 
times ten pounds of sulphur per thousand cubic 
feet of air space was used, to obtain a maximum 
of fumes in a minimum of time, and allow for 
leakage. 

Non-immunes stationed in the Canal Zone were 
advised not to visit the terminal cities except 
when absolutely necessary, because yellow fever 
was more prevalent there than in the Zone. Even 
the train schedule was changed on Sundays, to 
make it inconvenient for American employees from 
the Zone to remain long in the city of Panama. 
The object was to keep non-immunes away from 
the infected mosquitoes as much as possible. 

Two cases occurred in the Zone that were of 
special interest. The first was at Paraiso; the pa- 
tient was a locomotive engineer, and he had not left 
his home district except for about an hour and a 
half during the period in which he could have 
contracted yellow fever. On that occasion he had 
traveled three miles from Paraiso to Culebra in his 
engine cab, and arriving at Culebra, stepped out 
of his machine and into the pay car, where he 
remained only long enough to collect his pay. 
He at once returned to Paraiso with his engine. 
There was such a crowd moving about the pay car 
and its vicinity, it was not probable that any 



Campaign and Results 301 

Aedes calopus hovered in the vicinity, and there 
was no house near. 

No case of yellow fever had occurred at Paraiso. 
What was the source of infection? The histories 
of all cases that might be the source of the infection 
of the last case were reconsidered, and in point of 
time occurrence only one case seemed important. 
It was that of a peddler in the city of Panama, ill 
with yellow fever in the hospital. His history 
showed that he had not been to Paraiso, and on 
being questioned, he confirmed the statement. 
His friends corroborated it. The Paraiso case 
was still a puzzle. The patient's quarters at 
Paraiso, and adjacent houses, were fumigated to 
prevent secondary cases, and then the following 
action was taken. It was assumed that the 
possibility of infection at the pay car was too 
remote for serious consideration, and that some 
unknown infected person must have been to 
Paraiso before the engineer became sick. We 
visited every house, seeking for information, and 
received much confusing testimony. A second 
trip was made to determine if any stranger had 
been there to sell anything. We found that a man 
had been there selling trinkets similar to those in the 
above-mentioned peddler's box. It was finally 
proven that the Panama peddler had not only 



302 The Control of Mosquitoes 

been in Paraiso, but had rested in the shade on the 
porch of the house in which the American engineer 
slept. The peddler acknowledged this fact later, 
but refused to give any reason for his previous 
story. 

Another case of interesting history occurred in 
the city of Panama. A man was arretted for 
intoxication. While arguing with a policeman, he 
was seen by a sanitary officer, and sent to the 
hospital. Soon after arrival he became delirious; 
he proved to be a yellow fever case, and died that 
night, leaving only a fragment of his history. 
His statement, as far as it could be understood, was 
that he was a native of Greece, had no friends in 
Panama, and lived at a certain hotel. The hotel 
proprietor said he had never seen or heard of the 
man. For a day and a half the city was ransacked 
for additional information, without result. It be- 
came known that the hotel proprietor was not 
sure if the man had stayed at his establishment. 

Several men were employed to look up all the 
Greeks living in Panama. One of these learned 
that the case had been seen in an Italian cafe. 
The proprietor denied all knowledge of the fact. 
He was told that it would be necessary to close the 
cafe for a day for fumigation purposes, and he then 
volunteered the information that he knew the 



Campaign and Results 303 

deceased and knew that a fellow-countryman of 
his was a bartender at the old theater. A day's 
search located this person. He was in bed, sick 
with a pronounced case of yellow fever. He stated 
that he and his fellow-countryman had slept in the 
barroom of the theater. It was then too late an 
hour to fumigate the theater. It was closed and 
no performance permitted. The same night the 
daughter of the prima donna came down with 
yellow fever. She died a few days later. The 
data obtained showed a strong focus of infection 
at the theater, and this information prevented 
further spread of the disease. The theater was 
particularly dangerous, because non-immunes 
gathered there in numbers, and had infected Aedes 
calopus remained in the building they would have 
continued the infection. 

The last case of yellow fever in the Canal Zone 
occurred at Matachin on September 28, 1905. 
The patient was the station agent. The case had 
a number of interesting features. For two months 
previous to the attack he had never left the village. 
No other case of yellow fever had occurred recently 
in the Canal Zone, although a few had been found 
in Colon. This was the first and only case that 
occurred at Matachin. The only case that it 
corresponded with in point of infection was that 



304 The Control of Mosquitoes 

of a man at Colon who had never been to Matachin. 
However, the agent remembered distinctly having 
been bitten about the ankles and wrists while 
checking freight in cars that arrived from Colon. 
This is a characteristic biting habit of Aedes 
calopus. Subsequent investigation showed that 
these cars had been located on a siding at Colon 
near the house in which the case of yellow fever 
had occurred, corresponding exactly as to time of 
infection with the case at Matachin. 

At the time the yellow fever epidemic was 
coming to an end, the sewer system, water supply, 
and paving of the city of Panama were well under 
way. The old theory of the upturning of the soil 
being responsible for yellow fever was still believed 
by many. There was not a single case of yellow 
fever in the houses on or adjacent to the streets 
being torn up, nor in streets where trenches 
were being dug. Although the main water sup- 
ply distribution system was installed before yellow 
fever was eradicated, it had but little effect upon 
the suppression of this disease. Few houses 
were at that time supplied with plumbing fix- 
tures, and the native population preferred 
rain water, to which they were more accus- 
tomed. In subsequent years, as the houses be- 
came supplied with plumbing, less rain water 



Campaign and Results 305 

was collected, and rain water barrels were not 
allowed to exist. Of course this prevented the 
continuance of breeding places favorable to mos- 
quito development, and has been an important 
factor in keeping yellow fever out of Panama. 
Attention is invited to the fact that the city of 
Havana had an excellent source of water supply, 
and nearly all the houses in its yellow fever dis- 
trict had water taps in houses and yards long 
before the first American occupation. But a 
water supply alone, or even one supplemented 
by a proper sewer system, is not sufficient to 
control yellow fever or Aedes calopus propagation. 
In Havana, there was as much mosquito propaga- 
tion in houses occupied by Americans as in those 
occupied by natives. Systematic inspection by 
capable and energetic inspectors, working under 
a health officer especially trained for this work, is 
essential for yellow fever control. 



20 



CHAPTER VI 

MEASURES TAKEN TO KEEP THE ISTHMUS FREE 
FROM YELLOW FEVER 

A LL houses in the Canal Zone occupied by 
^^ American and foreign employees are not 
only screened, but the screening is kept in effective 
condition, inspected at frequent intervals, and 
repaired whenever defects occur. The lower parts 
of doors and all other screens subject to abuse are 
properly protected. All houses near settlements 
and adjacent territory are inspected each week 
for possible mosquito-producing containers. Any- 
thing that can hold rain water is removed, or so 
placed that water cannot remain in it. Foremen 
of gangs are ordered not to leave any material 
exposed that may collect rain water. Water in 
or on objects that cannot be moved, is treated 
with oil or larvacide. Tin cans and other waste 
material are buried. Where water is collected in 
barrels or tanks at isolated houses, these containers 

are made non-accessible to the mosquitoes. Tall 

306 



Preventive Measures 307 

grass is not allowed near settlements, as water con- 
tainers may become hidden under it. Interiors of 
houses are inspected to detect mosquito-producing 
containers, and tenants are invited to complain 
to the district sanitary inspector when mosquitoes 
are noted indoors. All houses are inspected for 
Anopheles at frequent intervals, at which times a 
keen search is also made for Aedes calopus. When 
adults of this species are noticed, very thorough 
inspection is made of all houses and yards in the 
vicinity. Each week the district inspector reports 
the number of Aedes calopus breeding places found 
during the regular weekly inspection, and notes 
their location in the station diary. As his district 
is inspected by the division inspector, the assistant 
chief sanitary inspector, and the chief sanitary 
inspector, any neglect of duty is soon detected. 
As a matter of fact, Aedes calopus are now very 
scarce near the settlements where the non-immunes 
live or spend their time. 

Attention is also given to movable containers. 
Whenever any large machinery or new supplies 
are moved into a district, they are inspected for 
parts capable of containing rain or other water. 
It has been found that certain types of tanks on 
locomotives and parts of certain dump cars hold 
rain water, and are capable of breeding Aedes 



308 The Control of Mosquitoes 

calopus. Such traveling containers can do much 
harm, as they may release mosquitoes at many 
places in a relatively short period. Many types 
of barges and canal boats contain and retain rain 
water. On one or two occasions they were known 
to have transported Aedes calopus twenty miles 
down the coast, from Colon to Porto Bello; adults 
appeared in large numbers in the settlement 
adjacent to the wharf to which the barge was 
tied, and in which this species had been absent 
for a long period. 

Although every precaution is taken to keep 
yellow fever out, it is always assumed that a case 
may enter at any time without the knowledge of 
the health authorities, and precautions are taken 
accordingly. The light cases known as "walking 
cases* ' are the most dangerous type. 

In order to keep a record of everyone coming from 
possibly infected areas, the chief sanitary officer 
keeps in touch with all infected seaports north 
and south of the Isthmus. Boarding houses and 
hotels are compelled to keep a correct register of 
guests, showing port of departure, and date of 
arrival of each, so that the history of any case 
may be rapidly obtained, and non-immunes 
associated with a case located at once and kept 
under observation. 



Preventive Measures 309 

Yellow fever is kept out of the Canal Zone and 
the cities of Panama and Colon by the following 
measures: Inspection of arrivals, quarantine sus- 
pects, and of all who have been less than six days 
in transit from ports where yellow fever is present, 
in order to complete the period of incubation of 
yellow fever under observation. For quarantine 
purposes this period is considered to be six days. 
In the ports of Panama-Balboa and Colon-Cristobal 
the quarantine officers board all vessels, and in 
addition to the usual examination and quarantine 
measures, detain those who appear at all likely to 
be suffering from yellow fever, and also all those 
who have boarded the ship at yellow fever ports 
less than six days from the day of the inspection. 

The careful exercise of quarantine regulations 
by vigilant, conscientious, and competent officers 
makes it unlikely that a case of yellow fever can 
land in a port, and be allowed to go at large. 

The three weak links in the chain are : 

1. An unrecognized case, in the early stages, 
might be allowed to go at large. 

2. A person in the early stages of yellow fever 
might land on the coast from some small vessel, 
and find his way overland into the Canal Zone, 
Panama, or Colon. This is possible, but ex- 
tremely improbable because it would be a mat- 



310 The Control of Mosquitoes 

ter of considerable difficulty to find a suitable 
landing place and then travel overland to some 
center of population. 

3. A ship might touch at a yellow fever port, 
and either take on a passenger there, and show 
him, by false entry on a passenger list, as having 
boarded at another port ; or allow some passengers 
or members of the crew to go ashore for awhile at a 
yellow fever port, and not make this fact known 
to the quarantine officers at Colon or Panama. 
While this would be a dangerous thing for the 
commander of a ship to do, one such case occurred 
at Colon. A ship of a well-known steamship line 
touched at a certain yellow fever port before com- 
ing to Colon. At Colon the captain subscribed to 
the statement that no one was allowed ashore 
while the ship remained in the yellow fever port. 
This statement was accepted by the quarantine 
officer at Colon, and the passengers allowed to 
land. 

Among the passengers was a young Englishman. 
Four days after his arrival he had an attack of 
yellow fever. Eight days later he was taken to 
Ancon Hospital where he died on the thirteenth 
day of the disease. Before he was taken to the 
hospital, throughout the period of infectibility, he 
lived in an apartment house in the city of Panama, 



M?f :*«&&,« 



Ik ^Tbt- *t»%*>. «» % «*l ¥*»«%' * * 





A short length of eave trough used over a doorway 



Preventive Measures 311 

boarded in a hotel, and mingled freely with people, 
many of whom were not immune to yellow fever. 
After the patient's removal, the usual precautions 
of fumigating were taken in the house in which he 
resided in Panama, as well as the house where he 
visited his sister, her boarding house, and a factory 
in which he had worked a few days. No other 
cases developed, because absolute reliance is not 
placed on quarantine alone, but on quarantine 
service supplemented by continuously sustained 
efforts for Aedes calopus destruction, which is the 
second and most important line of defense. 

As means of prevention of the reintroduction 
of yellow fever the following measures are adopted : 

Each house, garbage dump, cistern, well, water 
barrel, water-jug (tinaja), and other breeding 
places of Aedes calopus are inspected at least once 
a week. 

Breeding places that can be destroyed are 
immediately abolished, or notices are served upon 
the owners to destroy them within twenty-four 
hours . 

Wells, cisterns, water barrels, etc., which are 
more or less permanent, are protected against 
mosquitoes by screening with mosquito-proof 
metal screening. 

Troublesome eave gutters are cared for by 



3i2 The Control of Mosquitoes 

frequent inspections to detect sagging, etc., which 
tends to collect water. In practice it was almost 
impossible to maintain existing roof gutters on 
private residences in a self-draining condition 
except those placed over entrances and not exceed- 
ing eight feet in length. 

From time to time a wooden vessel holding a 
little clean water is exposed in a position convenient 
for ovipositing. The vessel is observed daily for a 
week or two to detect the presence of larvae in a 
given locality and reach a fairly definite con- 
clusion regarding their presence or absence. 

The methods adopted to keep the number of 
Aedes calopus on the Isthmus below the infective 
minimum and the results that have been accom- 
plished are due to the thorough and painstaking 
application of now well-known measures. It has 
been asserted that the eradication of such a pro- 
lific insect species as the Aedes calopus is impossi- 
ble. The senior author believes it possible; but 
for the practical purposes of the prophylaxis of 
yellow fever, entire eradication of Aedes calopus 
is desirable but not a necessity. What is needful, 
is to keep their number in a given locality below 
that required to propagate the disease. It is dif- 
ficult to determine what this number is. It would 
differ according to the number of fever cases 



Preventive Measures 313 

present; to the efficiency of the measures taken 
by quarantine for the exclusion of yellow fever; 
and to local conditions of housing. Each locality 
must establish its own rules in this respect. 

Discussion has arisen at intervals regarding the 
advisability of destroying water-holding plants 
such as banana, alocasia, etc. We are inclined 
to believe that danger from these plants has been 
greatly overestimated. It is possible that larvae 
of Aedes calopus may have been found in them, but 
careful observation in Cuba and on the Isthmus 
has convinced us that fully developed larvae or 
pupae of this species seldom occur in these water- 
holding plants, and that the banana plants are 
unimportant in producing them. The destruction 
of ornamental and useful plants causes opposition 
and we would urge that, before the wholesale 
destruction of these plants is undertaken, very 
careful observations be made to determine their 
true importance in the propagation of this 
mosquito. 



CHAPTER VII 

THE VALUE OF YELLOW FEVER ERADICATION IN THE 
CONSTRUCTION OF THE PANAMA CANAL 

A SIDE from the humanitarian aspect, the 
'**' value of the work lies in its practical 
aid to the problem before the people of the 
United States: the construction of the Panama 
Canal. Was the eradication of yellow fever 
essential to the solution of the problem of digging 
the canal? 

In reply three points must be considered: 

First, the loss of employees through the mortal- 
ity of yellow fever. 

Second, the effect of the presence of yellow fever 
on the morale of the corps of employees. 

Third, the effect of the presence of yellow fever 
on the canal on the attitude of the people and 
press of the United States and other nations 
towards the canal construction. 

The average number of employees on the canal 



Importance of the Campaign 315 

has been about 40,000, practically all of whom are 
non-immune. Their families residing on the Zone 
and in Panama and Colon would add approxi- 
mately as many more. If the yellow fever rate 
of the French company's employees is used as a 
basis for estimating the probable yellow fever mor- 
tality among the canal employees between 1905 
and 19 1 5 a mortality of about 1400 per annum 
among the employees would not err on the side of 
exaggeration. To this should be added at least 
an equal number for the employees ' families, were 
their families there. At this rate, during the ten 
years estimated for the completion of the canal, 
mortality from yellow fever would reach the 
frightful total of 14,000 employees, — 300 deaths 
for each mile of the canal. Even this estimate is 
based on the assumption that yellow fever in- 
creases in direct ratio with the increase of non- 
immune population, and that the number of 
cases of yellow fever progresses along a definite 
level, while in fact, the curve of yellow fever 
ascends much more rapidly than the curve of non- 
immune population; as knowledge of the mode of 
the transmission of yellow fever would premise. 

It is impossible to estimate even approximately 
the probable mortality from yellow fever had its 
devastation been left unchecked. 



316 The Control of Mosquitoes 

The effect on the morale of the employees. The 
presence of yellow fever in a community has a 
peculiarly depressing effect upon the non-immune 
inhabitants. Yellow fever is one of the diseases 
for which the human race may be said to have an 
inherited phobia. It is well known that in 1904- 
1905 special inducements were required to secure 
desirable men for work on the canal and even 
many of these soon left. We can testify from 
personal experience to the panic which cases of 
yellow fever occasioned among the American 
employees, many of whom returned to the United 
States within a few days after arrival, frightened 
away by the presence of yellow fever. It is 
obvious that the class of men who go to a yellow- 
fever-ridden country might not be the best from an 
economic point of view. 

The effect on the people and press of the United 
States, etc. The bulk of the laborers were re- 
cruited from Barbadoes, Jamaica, Trinidad, Spain, 
Italy, and Greece. Would these countries have 
permitted the emigration of a large number of 
their non-immune citizens to a country where 
yellow fever was rampant? Witness the action 
taken by these governments to prevent emigra- 
tion to the Manaos region, and Brazil region. The 
skilled labor, professional and clerical employees, 



Importance of the Campaign 317 

are American. Many people in the United States 
regarded the project, if not with hostility, then with 
indifference. The general mental attitude was 
that of judgment reserved, but with an underlying 
expectation that for one reason or another the 
Canal might not be completed. With several hun- 
dred cases of yellow fever among the employees, 
how long would the people of the United States 
have countenanced the construction of the Canal 
at such a price ? We think that had the method 
of yellow fever transmission not been discovered 
before 1904, and had it been impossible to eradi- 
cate it from the Isthmus, the Panama Canal would 
not be completed, as anticipated, in 19 14. 

Nor should another phase be forgotten. The 
work accomplished in Panama proved to the world 
the possibility of eradicating yellow fever from 
any locality where the work is properly conducted. 
Colonel Gorgas expressed his opinion regarding 
the eradication of yellow fever as follows : 



I look forward in the future to a time when yellow 
fever will have entirely disappeared as a disease to 
which mankind is subject, for I believe that when 
the yellow fever parasite has once become extinct, 
it can no more return than the dodo or any other 
species of animal that has disappeared from the 
earth. 



318 The Control of Mosquitoes 

At what cost can this work be accomplished? 
Many factors must be taken into consideration 
before even an approximate estimate can be 
attempted. The size of the community; the 
geographical and topographical features; the me- 
teorological data; the character of the water 
supply ; the method of sewage and refuse disposal ; 
the architectural characteristics of the dwellings; 
and the customs and habits of the natives, must 
all be considered. 

If it is desired to permanently rid a city 
of yellow fever, a complete water and sewer 
system should be installed, and all houses 
connected with them, to remove the necessity 
of having water containers in or near habita- 
tions. 

It is obvious that the cost of such a system must 
vary, and depend on local conditions, such as the 
size of the community, the distance from avail- 
able water supply and sewage disposal points, the 
cost of material and labor, etc. It is scarcely fair, 
however, to charge the cost of water and sewerage 
system to anti-yellow fever work exclusively, 
because these systems will benefit the community 
in many more ways than in aiding yellow fever 
eradication; some of the most obvious benefits 
being the reduction, if not the entire elimination, 



Importance of the Campaign 319 

of water- and fly-borne diseases, of the cost and 
trouble to the individual householder in obtaining 
and maintaining a private water supply, and 
refuse disposal plant, and also in protection from 
fire with all the gain the last item carries with it 
in the way of reduced insurance rates, business 
development, etc. 

The cost of maritime quarantine, if necessary in 
a given community, should also not be charged 
entirely to anti-yellow fever work. Maritime 
quarantine will benefit the community in many 
ways, by excluding undesirables and carriers of 
various infectious diseases. Only a portion of this 
expenditure, say one fourth, can be justly charged 
to anti-yellow fever measures. 

Assuming that an anti-yellow fever campaign 
were to be inaugurated in a city similar to Panama, 
a city of 40,000 inhabitants, covering an area of 
approximately one square mile; with a well- 
marked rainy season of eight months' duration 
and Aedes calopus breeding all the time; with 
yellow fever foci within six days' travel, and being 
in constant communication with the city ; with no 
communal water and sewer system, and with yel- 
low fever cases present, the following preliminary 
organization would be desirable for an anti-yellow 
fever campaign : 



320 The Control of Mosquitoes 

Preventive Organization 

Per Month 

I health officer $ 300.00 

1 assistant health officer 250.00 

3 clerks 250.00 

8 inspectors 1 ,000.00 

10 foremen 350.00 

100 laborers 2,500.00 

7 wagoners 225.00 

$4,875.00 

7 wagons $ 250.00 

14 mules 2,000.00 

14 sets of harness 450.00 

$2,700.00 

Material necessary: Ladders, sulphur, pyre- 
thrum, alcohol, paper, one-inch strips of wood in 
lengths of six to twelve feet, tacks, tools, oakum 
or cotton waste for calking, canvas for tentage, 
cords, pans for fumigation, brushes for pasting, 
flour for paste, scrubbing brushes for removing 
the adherent paper, soap, wire gauze, spigots, and 
barrel tops. 

The hospital organization: A fifty-bed hospital 
of small wards preferably. Double-screened 
vestibules, with the doors arranged so that only 
one door can be opened at a time and a watchman 
constantly on duty to see that both doors are 



Importance of the Campaign 321 

never opened at the same time. The hospital 
personnel should consist of: 

2 physicians $450.00 

15 nurses (1 chief nurse) 1,100.00 

25 orderlies, etc 400.00 

1 druggist 150.00 

1 clerk 125.00 

2 cooks 100.00 

1 ambulance driver 50.00 

$2,375.00 

1 ambulance with appurtenances $1,200.00 

Subsistence of patients at $1.00 per day per patient. 

The Quarantine Organization 

1 quarantine officer $ 300.00 

1 assistant quarantine officer 250.00 

1 launch engineer 75-00 

1 launch hand 30.00 

1 custodian of quarantine 

station 125.00 

$ 780.00 XX = $195.00 

and the necessary attendants, waiters, etc., re- 
quired for the detention house, which should pay 
a considerable portion of its maintenance from 
the fees collected from the passengers. 

Calculating the cost of this organization on the 
basis of salaries paid in Panama by the United 



21 



322 The Control of Mosquitoes 

States, the cost chargeable to the anti-yellow fever 
campaign would be as follows : 

For salaries and wages about $7500 per month. 

For material, etc., $3000, inclusive of cost of 
maintenance of hospital and one quarter the cost 
of the maritime quarantine, but not including that 
of water and sewer installation. 

The campaign in Panama lasted approximately 
fourteen months. It is the opinion of the chief 
sanitary inspector, who conducted the campaign, 
that this time could have been reduced to six 
months had supplies been more readily available, 
together with active cooperation on the part of 
the civil authorities. Assuming that the prelimi- 
nary work could be completed in nine months, the 
cost of the 

Preventive Organization would total $57,400.00 
Hospital Organization would total 34,875.00 

$92,275.00 

After this period, only a small fraction of the 
time of the health officer and his organization 
need be given to anti-yellow fever work, and the 
organization could be reduced or Hs activities 
directed into other channels. 

The hospital could be converted into a general 



Importance of the Campaign 323 

hospital, or closed. The quarantine organization 
should remain permanent. 

It is to be understood that the figures given are 
merely approximate, and based on the cost in the 
city of Panama. This estimate is subject to wide 
variations under varying local conditions. 

Yellow fever was eradicated in towns in Cuba 
without the installation of sewer and water supply. 
In the absence of these conveniences, it will 
depend upon the conscientious work of those in 
charge of the mosquito- control campaign whether 
fever will be reintroduced. At Santiago de las 
Vegas, Cuba, a town of about 10,000 inhabi- 
tants of which ten per cent, were non-immunes, 
yellow fever was eradicated and mosquito breed- 
ing places eliminated within three months at a 
cost of less than $5000. 

In that case the chief sanitary officer was well 
supported by the governor and town officials. 

In 191 1, in reply to a question relating to the 
world's greatest events, the Right Honourable 
James Bryce, Ambassador to the United States, 
said : In modern times most of the events of high- 
est ultimate significance have been discoveries in 
the realms of nature or inventions in the realm of 
industry; and their magnitude is seldom known 
at first. Little was said of the discovery that 



324 The Control of Mosquitoes 

mosquitoes are the carriers of yellow fever and 
the intermittent fevers, yet what immense conse- 
quences are already seen to flow from the determi- 
nation of that fact! 



INDEX 



Acetylene lamp for mosquito 

catching, 91, 211 
A'edes calopus, biting experi- 
ments, 234 

biting habits of, 304 

collection of dead, 241, 

277 

container breeders, 55, 

240 

control of, 235 

detection of, 312 

eradication of, 234, 241, 

291, 312 

flight of, 234, 242 

habits of, 234, 240 

infection of, 245 

larvae, habits of, 263 

period of incubation, 235 

time of biting, 274 

Agramonte, Dr., experiments 

in Havana, 231 
Algae, copper sulphate applied 
to, 45 

larvae found in, 47 

matted with crude oil, 61, 

71, 170 

penetration by larvae, 65 

protect larvae, 26, 65, 180 

rapid development of, 26 

retards currents, 60 

warmth increases growth 

of, 65 m 
Ancon Hospital, before 1904, 
16, 18 

mortality statistics, 265 

preventive measures 

adopted at, 283, 287 
Anopheles, avoidance of light 
by, 22, 51, 84, 94 



Anopheles, biting experiments 

with, 21, 46, 89 

biting in sunlight, 78, 90 

in brackish water, 74 

carriers, animals, 92 

boats, 308 

cars, passenger and 

freight, 92 

travelers, 50, 51, 92 

caught after staining, 114 

characteristics of larvae, 

5,222 
collection of larvae and 

pupae for laboratory, 45, 

46 
in cracks of hydraulic 

fills, 120 

deprivation of air, 152 

destruction by hand, 52, 

186, 202, 208, 220 

evaporation fatal to, 46 

flight, against the wind, 95 

at Gatun, 76, 98 

long distance, 47, 96, 

98, 100 
in relation to rain- 



fall, 38 

time of, 188 



hiding places of larvae, 62 
in hospital wards, 20 
hours of biting, 21, 85, 

89,224 
identification of larvae, 48 
lack of data concerning, 

43, 44, 73 

larvae, methods of detec- 
tion of, 78 

long distance transporta- 
tion, 50, 92 



325 



326 



Index 



Anopheles, methods of stain- 
ing, no 

■ prevalence of, before sani- 
tation, 20 

prevalence of, at Gatun, 

1913, 98 

propagation areas, 43, 64 

sheltering habits, 86 

time of collecting on 

screening, 51, 213 

Anophelines of the Canal 
Zone, 51 

habits of, 47, 91, 196 

persistence of, 52, 204 

Ants, natural enemies of mos- 
quitoes, 186 

Apparatus to register flight of 
mosquitoes, 108 

Aquatic insects, natural ene- 
mies of mosquitoes, 185 

Aquatic plants, 10, 40, 97, 
129, 182, 190 

change in character of, 

190 

in Gatun Lake, 99 

protect larvae, 40 

reduce stream flow, 10, 29 

reduce surface velocity, 

10 

Army Medical Board, con- 
clusions of, 233, 235 



Bath, Mr., mosquito trap, 216 

Bats, natural enemies of mos- 
quitoes, 188 

Bermuda grass, 193 

Birds, natural enemies of 
mosquitoes, 188 

Birds, "night- jars," 102, 104, 
106, 188 

Birds, water-fowl, 41 

Blood samples, taking of, 18 

Boats as carriers of malaria, 
308 

Boats, for clearing rivers, 64, 
196 

flat-bottomed, for oiling, 

168 

Borrow-pits {see fills) : 



Breeding places, of A. albi- 
manus, 47 

in borrow pits, 70 

clearing promotes evapo- 
ration of, 195 

crab holes, 72 

excavations, 40, 70 

puddles, 25 

railroad tracks, 38 

rivers in dry season, 64 

stream-beds, 62, 63 

streams on steep hillsides, 

25 

temperature of water in, 

72 

Bryce, Right Honorable James, 

323 

Busck, A., of Smithsonian 
Institute, 44, 53 



Cages, for Anopheles transpor- 
tation, 46 

for fumigation tests, 252 

for immersing larvae, 50, 

152 
screened, for yellow fever 

patients, 288 
for staining Anopheles, 

no 
Campho-phenique (see Fumi- 

gants) 
Camps, near Bas Obispo River, 

183 

selection of sites, 226 

for troops in tropics, 220 

"Canal Building," screening 
of, 282 

yellow fever focus, 280 

Carroll, Dr., experiments in 
Havana, 231 

Cars, screening of, 203 

Carter, Dr. H. R., observa- 
tions on time of incubation, 
231,235 

Case histories, 300 

to determine sources of 

infection, 244, 308 

Panama, 285 

Catch basins in sewers, 157 



Index 



327 



Chloroform tube for mosquito 

catching, 91, 211 
Clothing for rainy season, 81 
Collecting Anopheles larvae and 

pupae for laboratory, 45 
Colombia, lack of sanitary 

organization, 264 
Concrete (see Ditches) 
Containers, the breeding places 

of Aedes calopus, 55, 240 

dregs in, 263 

experimental wooden, 312 

flower-pots at Ancon 

Hospital, 18, 263 

hidden, 241, 280 

mosquito producing in 

Havana, 237, 240 

mosquitoes disappear on 

removal of, 290 
movable and traveling, 

307 

resembling natural breed- 
ing places, 55 

in rubbish heaps, 263 

screening of, 311 

Coral formation, 7, 269 
Costs of Canal Zone prevention 

measures, 220 
Crab holes, 72 
Culverts (see Drainage) 



Darling, Dr. S. T., biting 
experiments by, 46 

identification of larvae by, 

48 
studies of Isthmian Ano- 
pheles, 45 
Diary, station, 307 
Ditches, alignment of, 146 

branch, 126, 134, 141, 143 

comparative cost of lin- 
ings, 137, 145, 148 

concrete lining, 136 

conditions producing mos- 
quitoes, 71 

cost of spoiling grade, 147 

factors in construction 

of, 149 
fieldstone lined, 19 



Ditches, grading of, 126, 128, 
132, 134, 147 

herring bone, 7, 126 

on hydraulic fills, 120 

inspection of, 129, 144, 

145 

intercepting, 9, 16 

key walls, 140 

location of, 125, 196 

maintenance of, 125, 144 

cost of maintenance of, 

15, 137, 145 

masonry lined, 1 7 

narrow bottomed, 125 

natural water-courses, 149 

near seepage outcrops, 136 

open, 125, 129, 130, 136, 

149 
permanent lining of, 8, 

137 

pot-holes in, 61, 125, 128 

regrading of, 130 

reinforced concrete lining, 

I5.I38 
reinforced concrete lining, 

cost of, 138 

scouring of, 128, 130 

slope of, 125, 136, 138, 

140, 144, 148 

soft bottomed, 56, 148 

storm water, 127 

in truck gardens, 11 

undermining of, 41, 143, 

144, 146 

width of, 123, 143, 148 

weep holes in, 136, 139, 

141 
Dragon flies, 185 
Drains, outlet of intercepting 

tile, 135 
Drains, storm water, 127 
1 ' Drainage, A nopheles, ' ' re- 
quirements for, 125 
Drainage, badly planned, 124 
channels, blocking of, 

.39 

in coral formation, 7 

culverts, 41, 70, 150 

use of dynamite in, 118 

grade, change of, 131, 149 



328 



Index 



Drainage, grade, to fit topog- 
raphy, 141 

flatness of, 72, 125 

steepness of, 128, 

132 

taking levels for, 126, 

132 

open, 125 

pipe lines for, 149 

subsurface, cost of main- 
tenance, 134 

tile, 130, 132 

intercepting tile, 131, 134 



"Drips" (see OH) 

Eave-troughs, 262, 289, 311 
Employees, mortality of, 314 
Enamel-ware saucers and dip- 
pers, 45, 79 
Evaporation of cleared spaces, 

12, 195 
Excavations, 70 

Fills, on absorbent ground, 115 

borrow pits for, 116 

heavy, 118 

hydraulic, cost of, 121 

cracks in, 119 

filling cracks in, 120 

shallow ditches on, 

120 

porous material for, 116 

settling of, 39 

shallow, 116 

vegetation on, 118 

Fines, sanitary regulations, 239, 

275 
Finlay, Dr. Carlos, theory of 
yellow fever transmission, 

.231,235 

Fire, clearing by, 197 

danger from stored oil, 

165,171 

precautions in fumiga- 
tion, 248 

Fish, Barbadoes, 185 

used after clearing and 

training, 10 

notes on, 64, 184 



Fish, small, cannot penetrate 

algag, 65 
value as eradicators of 

larvae, 182, 191, 194 

value as eradicators in 

i New Jersey, 185 
— ; — in wells, 8 

Flight, apparatus for register- 
ing, 108 
solution for registering, 

108 
(see Aedes calopus and 

Anopheles) 
Floating islands, drifting of, 

99, 194 

Fomites, yellow fever, 233, 236 
Foot-prints, holding water, 60 
Formula for drip oil, 159 

Panama larvacide, 174 

pumping oils, 167 

stain, in 

stain testing solvent, in 

French occupancy of Canal 
Zone, statistics, 23 

villages and camps, 17 

Fumigant, campho-phenique, 

254 

formaldehyde, 253 

pyre thrum, 254 

pyrethrum, deterioration 

of, 253 

sulphur, 254, 300 

tobacco, 253, 254 

Fumigation, action on fruit 
cargoes, 258 

Ancon Hospital Reserva- 
tion, 283 

brigades in Havana, 243, 

245 

brigades in Panama, 284 

city of Panama, 284 

experiments in Havana, 

250 

methods of, 246 

pans, 247, 258 

system of, 236, 244, 252, 

286 

tests, 251 

of theater, 303 

uncertainty of, 290 



Index 



329 



Fumigation of vestibule at 
Ancon Hospital, 287 

after yellow fever cases, 

244, 286 

Geography of the Canal Zone, 
268 

Gorgas, General W. C, anti- 
malaria work before 1904, 3 

appointed by President 

Roosevelt, 16 

Aedes calopus destruc- 
tion in Panama, 235 

on disappearance of yel- 
low fever, 317 

eradication of yellow fever 

in Havana, 231 

Ordinance 6, 273 

— — pamphlet, 1906, 265 

physicians' reports, 243 

preparations for cam- 
paign in Panama, 272, 

293 

rapid selection and de- 
livery of supplies, 272, 

273 

report to General Leonard 

Wood, 232 
report on Isthmian Canal, 

1904, 261 
Grade (see Drainage and 

Ditches) 
Guard, at door of "Canal 

Building," 281 
at door of yellow fever 

ward, 320 
at residences of yellow 

fever patients, 244, 286, 

287 

Hand catching, (see A nopheles) 

Hoof -prints, 19 

Anopheles propagation in, 

10, 71, 146 
difficulty of treating with 

oil, 56 

filling, 115 

of horses with mowers, 

197 



Hoof-prints, sanitary regula- 
tions, for 57 

Hospital organization, a plan 
for, 320 

Hotels and boarding houses, 
sanitary regulations for, 308 

House flies, fumigation effects 
on, 251 

Howard, Dr. L. O., suggestions 
and advice in Panama cam- 
paign, 44 

on oil for mosquito de- 
struction, 235 

writings of, 236 

Hydraulic fills (see Fills) 

Infection of Aedes calopus, 284 

from seaports, 308 

Inspection, checking system, 

2 39„ 
of ditches, weekly, 129, 

144 

of fumigation, 247, 250 

house to house for Aedes 

calopus larvae, 237, 274, 

278 
of houses weekly for 

Aedes calopus larvae, 

276 

of oil drips, 161 

of quarantine suspects, 

309 

of screening, weekly, 205 

systematic, 305, 307 

system of, in Havana, 6, 

236 
yellow fever campaign, 

Panama, 274 

of yellow fever wards, 287 

Inspectors, efficiency of, 59, 
305 



report forms, 238 

responsibility of foreman, 

147 

Jennings, A. H., collections of 

Zone mosquitoes, 44 
Jungle, cleared from camp and 

town sites, 195 



330 



Index 



Jungle, cleared from abandoned 

French camps, 22 
unexplored, 22 t 125 

Kendall, on fumigation, 254 
Key walls {see Ditches) 
Knab, F., determination of 
species of Isthmian mosqui- 
toes, 45 

Labor, class allowed Sanitary 

Dept., in Panama, 298, 299 

high cost of, prevents 

progress in the South, 

221 

intelligent, at Havana, 6 

non-immune, infection of, 

39 

shortage of, in malarial 

districts, 219 

transportation of, in 

ambulances, 246 
transportation of in cov- 
ered wagons, 5 

ultimate cost of infection 

of, 42 
Laborers, barracks, 213 
Larvacide as a detective, 79 

Panama, advantages of, 

172, 176 

cost of, 174, 177 

formula for, 174 

process of manufac- 
ture, 175 
toxicity of, 152, 176, 

requirements for, 173 

Larvacides, comparative values 

of, 151 
Larvae (see A'edes calopus and 

Anopheles) 
Lazear, Dr., yellow fever 

experiments, 231 
Legislation, Panama, 243 
Le Prince, J. A., discovery of 

mosquito flight, 103 

report to International 

Congress of Hygiene, 
1912,95 



Light, effect on mosquitoes, 

94, 97, 253 
Light and dark, effect on 

mosquitoes, 186 
Lizards, 186 
Low, Dr. G. C, observations at 

Ostia, 198 

Machetes, use of, 195 

Malaria developed by excava- 
tion and settling of fills, 39 

control, effect of topo- 
graphy and climate on 
cost of, 165 

control, avoidable costs, 

70 r 

cost of preventive mea- 
sures in the Canal Zone, 
220 

effect on labor cost, 219, 

221 

infection, effect of screen- 
ing on, 206 

infection of United States 

agricultural population, 
219,221 

mortality statistics in 

Havana, 13, 14 

mortality statistics, city 

of Panama, 23, 24 

in native population, 

Panama before 1904, 
16, 18 



at old Ancon Hospital, 20 

parasite, 47 

pernicious, 8 

prevents development of 

the tropics, 42, 220 

prevention, need for sani- 
tary regulations for, dur- 
ing engineering work, 
38, 70, 116 

rate in the tropics, 219 

transmission of, 51 

United States Public 

Health Service reports, 

.24 „ 

Materials for a plan of cam- 
paign, 320 
Materials, storehouse for, 245 



Index 



33i 



Monel metal, mosquito wire, 

224 
Mortality statistics, city of 

Panama, 23, 24 
under French occupancy, 

23 
Mosquito bars, 20, 46, 89, 

112, 274, 288, 296 
Mosquito catching in dwellings 
as a prophylactic measure, 
202, 208 

in screened cars, 210 

destruction in Havana, 

236 
Mosquitoes, artificial producing 

areas, 41 
biting experiments, 89, 

91,92 

carried on clothing, 187 

change of species, J2 

collection of dead, 250 

collecting and staining, 

112 

flight observation, 76 

hiding places of, 36 

hidden producing areas, 9 

hours of biting, 21 

infective minimum, 312 

Isthmian climate favor- 
able to, 268 
larvae, destruction by 

aquatic insects, 185, 191 
natural enemies of, 185, 

191 
sudden influx at camps, 

155 
trap for, 96, 214 

Oil, application of, 171 

rule for application of, 

163 

carts, 168 

cost of distribution, 164, 

165, 166 

low cost of crude, 153 

drips, barrels, 159 

for heavy and light 

oils, 160 

inspection of, 161 

notes on, 154, 225 



Oil drips on rafts, 156 

on streams, 155, 156 

films, 154, 162, 171 

breaking of, 71 

drifting of, 170 

spreading of, 190 

heavy, inhibits vegeta- 
tion, 171 

how it kills larvae and 

pupae, 151 

and larvacide for pumps, 

166 

methods of distribution, 

164 

pipe lines for, 164 

spraying, 166 

tanks, 164, 168 

viscidity in lower tem- 
perature, 157 

Oiling, from boats, 168 

continuous, 154 

costs of, 171 

cotton waste in drip can, 

application by cotton 

waste, 161 

drips for light oils, 160 

intermittent, 162 

at irregular intervals, 6, 

12 
by "knapsack sprayer," 

166 

methods of, 154 

precautions for floods, 161 

simplest form of drip, 158 

treatment at Havana, 5 

with watering can, 168 

Orenstein, Dr. A. J., prophy- 
lactic value of screening, 206 
Outlet of tile drain {see Drain) 

Pack mules, for transporation 
of oil, 169 

Panama population near ende- 
mic sources of yellow fever, 
262 

Preventive organization, a 
plan for, 320 

Pipe lines for distribution of 
oil, 164 



332 



Index 



Pipe for drainage, 149 

screening entrances of, 

*49 . . 

Plan of campaign, estimated 
cost, 321 

Plants, water holding, 72 

Porto Bello, reintroduction of 
Aides calopus, 308 

Pot-holes (see Ditches) 

Potato hooks, to uproot aquat- 
ic plants, 192 

Proctor, Mr., mosquito trap, 
216 

Prophylactic inoculation of 
yellow fever, 241 

Pumps for oiling, 166, 168 

Pyrethrum, fumigant, 247, 254 

Pyrocresol, larvacide, 178 

Quarantine, cost of maritime, 

a plan for organization, 

3i9,3 2 i 

precautious, 308 

suspects, 309 

Quimby, E. F., apparatus for 
registering flight, 107 

f 

Rainfall, charts, and topo- 
graphy, 27 

continuous, effect of, 23, 

58 
continuity compared with 

volume, 33 
heavy showers remove 

larvae, 11 

effect of sudden, 61 

variations of, 59 

Real estate values affected by 
mosquito control, 3, 10, 121, 

319 
Reed, Dr. W., experiments m 

yellow fever transmission, 

231 
Reinforced concrete (see 

Ditches) 
Research required, 69, 223 
Reservoirs, clearing of, 68 

preparation of sites for, 

193 



Rivers, blocking of, 70 

Rivers, mosquito control on 
the Rio Grande, 64 

Rock, decomposition of, at 
Culebra Cut, 118 

Roosevelt, President, appoint- 
ment of Colonel Gorgas, 16 

Ross, Sir Ronald, anti-malaria 
work in the East, 3, 5 

Prevention of Malaria, 151 

Sambon, Dr. L. W., observa- 
tions at Ostia, 198 

Sanitary regulations, compul- 
sory reports of fevers in 
Panama, 285 

— - fines, 239, 275 

hotel and boarding house 

registers, 308 

impounding cattle, 57 

need for, during engineer- 
ing work, 70, 116 

Ordinance 6, 273 

physicians' reports at 

Havana, 243 

in Panama treaty, 272 

Santiago de las Vegas, cost 
of yellow fever eradication, 

323 . . 

eradication of yellow 

fever, 243, 291 
Screening of cars, 203 

city of Panama, 277 

copper gauze, 198 

crevices in perfectly 

screened buildings, 204 
doors, 87, 199, 201, 280, 

306 

imperfect, 204 

inspection by Health 

Dept., 205 
metal, composition of, 

199, 207, 224 

metallic, 206 

position for doors, 87 

protection of, 201 

repairing of, 205, 306 

of sick-rooms, 244 

of tents, 203 

verandas, 199 



Index 



333 



Screening vestibules, 201 

water-barrels, 279, 293 

windows, 200 

Seasonal changes, effect on 
mosquito production, 44 
68, 72, 81, 112, 126 

Seepage, location of, 126 

notes on, 65 

outcrop, Ancon, 19 

Havana, corrected 

by gravel and cin- 
ders, 8 

outcrops between lines 

of tile, 135 

covered by vegeta- 
tion, 196 

on hill side, 37 

permanent and in- 
termittent, 131 

on stream banks, 36 

in unusually rainy 

years, 127 

planes, 116 

sharp changes of grade, 66 

Sewerage, catch basins in, 157 

, installation in Panama, 

288 

Slapper, for mosquito catching, 
212 

Species, change of, Anopheles, 

72 . . 
determination of, 45 

Spiders, 186 

Spraying, methods of, 166 
Spray-nozzle, 167 
Staining of Anopheles, 110 
Station, experimental, for ma- 
laria transmission data, 25 
Stations, meteorological, 31 
Stream-beds, erosion of, 35 
Streams, branch, 36 
and drains, blocking of, 

39 

"drips "on, 155 

on hillside, carriers of 

larvae, 35 
on hillsides, changes of 

source, 62 

as oil carriers, 155, 161 

pot-holes in, 36, 61 



Streams, regrading of, 130 
as sources of mosqui- 
toes, 35, 60 

training of, 7, 63, 141 

Subsurface drainage, {see ) 

Drainage) 
Sulphur, fumigant, 253, 254 
Supplies, importance of rapid 
delivery, 21, 272, 273, 246 

system of preparation, 

245, 246 

■ torehouse for, 245 

Surveys, preliminary, 16, 22, 

25, 126 
Susceptibility to bites, 85, 91, 

93 

System of checking inspections, 

239 

Tadpoles, 185 

Temperature of water, effect 

of, 65, 66, 72 
Tent hospitals, 204 
Tents, screening of, 203 
Tides, low lands near coasts 

affected by, 25, 75 
Tides in Rio Grande valley, 75 
Tile drainage (see Drainage) 
Tile drains, inspection of, 135 
Tobacco, fumigant, 253, 254 
Topography, changes in, 6, 

38, 145 

Topography, cause of difficulty 
in mowing, 197 

Trask, H. R., cart for oiling, 
168 

Treaty, United States and 
Republic of Panama, sanita- 
tion clause, 272 

Trees, in flooded areas, 63, 72, 

75,193 . . 

Truck gardens, irrigation of, 
11 

United States Public Health 
Service reports, 24 

Vegetation breaks oil film, 190 
burning of, 118, 197 



334 



Index 



Vegetation, changes in, 182 
clearing of, from water, 

63, 191 

cutting on edges of 

streams, 10, 64 

grass cutting, 295 

effect of dead, 79 

on fills, 39, 118 

inhibition of, 171, 177, 

192 

retards current, 129, 130 

retards surface velocity, 

10 

on seepage outcrops, 196 

shelters mosquitoes, 43 

toxic effect of Panama 

larvacide on, 177 
uncut, retards evapora- 
tion, 37, 197 
Verandas, screening of, 199, 

202 
Vestibule, on houses of yellow 

fever patients, 286 
yellow fever ward, 287 

Walking cases (see Yellow 

fever) 
Water barrels, mosquito proof- 
ing of, 293 m 

impounding of, 150 

near sewer outlets, 81 

subsurface, 116 

supply, effect on yellow 

fever in Panama, 262, 
269, 288, 304 

in French camps, 17 

in Havana before 

yellow fever cam- 
paign, 305 

notes on, 318 

in towns in Cuba, 

323 

temperature of, in relation 

to Anopheles produc- 
tion, 65, 66, 72 
velocity of, effect on 



larvae, 144, 149 
Watson, Dr. Malcom, report 
to Royal Colonial Institute, 
225 



Wave action, effect on mosqui- 
to larvae, 68 

ripples break oil films, 

163, 170 
Weep holes (see Ditches) 
Wells, Anopheles in, 55 

in coral formation, 7 

Wheel- tracks, filling of, 58, 115 
Wind action, loss of fumes by, 

259 

moves and collects debris, 

68 

Anopheles travel at right 

angles to, 105 

Anopheles rest under 

houses during, 86 

breaks, 170 

drying effect on mosqui- 
toes, 46, 113 

effect on larvae in lakes, 

etc., 68 

evaporation of flat areas, 

12 

velocity of, 86, 90 

Wood, General Leonard, sup- 
ported mosquito control 
measures in Cuba, 242 

Yellow Fever Board, Panama, 
286 

a plan of campaign 

against, 320 

cases, 243, 275 

investigation of cases and 

suspected cases, 283 

case histories, 300 

chain of transmission, 292 

Commission, Cuba, 246 

cost of eradication, 318 

effect on emigration, 316 

effect on morale of em- 
ployees, 314, 316 

eradication, 291, 314, 317 

eradication without sewer 

and water supply, 323 

foci, 265 

fomites, 233, 236 

history of, 232 

imported cases, 292 

infection, 245 

mortality curves of, 315 



Index 



335 



Yellow fever, mortality statis- 
tics in Panama, 264 

old theory of, 304 

panic, 316 

parasite, 317 

period of incubation, 233, 

309 

phobia, 316 

a plan of campaign with 

costs, 319 
prophylactic inoculation 

of, 241 
reintroduction of, 291, 

3ii 
subsidence of, with ex- 



haustion of non-im- 
mune material, 267 

Yellow fever, "suspects," 241, 
246, 283, 286 

transmission, 232, 292, 

298, 323 

on United States Cruiser 

Boston, 276 

"walking cases," 245, 

283, 308 

wards, Ancon Hospital, 

287 

Zetek, J., marking and staining 
mosquitoes, 107, no 



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